Will Smith and Jaden Smith riding a bus in The Pursuit of Happyness

It's always fascinating when actors who are related in real life share the screen. But sometimes, those actors are also related in the exact same way as the characters they're playing are, and it's amazing.

This adds a layer of realism to the film or TV show. Actors who are related look like each other in a way Hollywood just can't fake. Plus, it can make the acting process more natural. After all, a brother and sister who are playing brother and sister are bound to give realistic performances. Sometimes actors who are related use this familial bond to create performances that have autobiographical elements to them.

It's relatively common for the young children of actors to play their parents' kids on screen. After all, these kids are often new to acting and are already comfortable with their parents. Many kids have gone from roles like these to becoming actors in their own right.

On this list, you'll also find siblings and spouses playing characters who are actually siblings and spouses. Here are 15 Movie Families You Didn't Know Were Actually Related.

15. John Cusack and Joan Cusack - Say Anything

John Cusack as Lloyd Dobler and Joan Cusack as Constance in Say Anything

These siblings have acted together in films like High Fidelity, Broadcast News, Grosse Point Blank, and Sixteen Candles. Their characters often have quality screen time with each other. In Grosse Point Blank, John plays a professional assassin and Joan plays his secretary. In High Fidelity, he plays record store owner and Joan plays his friend.

They played siblings in Cameron Crowe's classic rom-com Say Anything... (1989). Joan is the older sibling in real life, and she's the older one in the movie too. John Cusack plays the romantic Lloyd Dobler, who falls for his classmate Diane Court (Ione Skye). Joan plays his sister Constance, a single mother with a young son. They have a great working relationship.

On working with her brother, Joan told SheKnows, "You are not worried. You're not distracted. You get to trust your instincts. My brother does not let me look bad. ...I believe in John and his passion."

14. Charlie Sheen and Martin Sheen - Wall Street

Charlie Sheen, Martin Sheen, and Michael Douglas in Wall Street

Martin Sheen and his son Charlie Sheen are both well-known actors, and they've shared the screen in films and TV shows including Cadence, No Code of Conduct, and Free Money. They were also both in the documentary 9/11: Truth: Hollywood Speaks Out. In fact, Charlie Sheen's first few credits came from appearing as an extra or playing bit parts in three Martin Sheen films: Badlands, The Execution of Private Slovik, and Apocalypse Now.

The pair played father and son in Wall Street (1987). The plot follows Bud Fox (Charlie Sheen), a junior stockbroker on Wall Street who's willing to cheat to get to the top. Martin Sheen plays his father Carl, a blue-collar maintenance foreman and union leader.

Martin Sheen also played Charlie Sheen's dad on Charlie's TV series Anger Management, appearing in 20 episodes. Martin Sheen played his son's dad on another of Charlie's TV shows, Spin City, which Charlie acted on from 2000 to 2002.

13. Jake Gyllenhaal and Maggie Gyllenhaal - Donnie Darko

Jake Gyllenhaal as Donnie Darko and Maggie Gyllenhaal as Elizabeth Darko in Donnie Darko

Siblings Jake and Maggie Gyllenhaal grew up in a Hollywood family: their mother Naomi Foner Gyllenhaal is a film producer and screenwriter and their father Stephen Gyllenhaal is a director. Jake and Maggie both started acting in the early '90s.

These famous siblings played brother and sister in Donnie Darko. Jake plays the titular troubled teen, and Maggie has a supporting role as one of this two sisters, Elizabeth. During a squabble, Donnie and Elizabeth have this memorable exchange:

Elizabeth: You can go suck a f--k.

Donnie: Oh, please, tell me, Elizabeth, how exactly does one suck a f--k?

On working with his sister in Donnie Darko, Jake told The Guardian, "There is truth in the scenes when we're fighting, because that is what we were going through at that time. If we did a movie now it would be completely different. More and more we're getting to be comrades." His starring role in Donnie Darko brought him critical attention and Maggie caught the world's eye a year later for her starring role in Secretary.

12. Henry Fonda and Jane Fonda - On Golden Pond

Henry Fonda as Norman Thayer and Jane Fonda as Chelsea in On Golden Pond

On Golden Pond follows an elderly couple, Norman and Ethel Thayer, who are spending the summer at their cottage on Golden Pond and are visited by their estranged daughter Chelsea. Norman has always been a curmudgeon, but on top of that, he's starting to lose his memory. The 1981 film starred Henry Fonda as Norman, Jane Fonda as Chelsea, and Katharine Hepburn as Ethel. It was based on the 1979 play of the same name by Ernest Thompson.

According to The Age, Jane Fonda bought the rights to the play specifically to offer the role to her father. The relationship between Norman and Chelsea Thayer paralleled the real-life relationship between Henry and Jane Fonda. Their strained relationship started early: when Jane was growing up, her father made her think that looks were all that mattered, and as a result, she developed bulimia. Henry Fonda won his first Oscar for the film.

11. Elizabeth Taylor and Richard Burton - Who's Afraid of Virginia Woolf?

Elizabeth Taylor as Martha and Richard Burton as George in Who's Afraid of Virginia Woolf?

Playing Martha and George in Who's Afraid of Virginia Woolf? must have put Elizabeth Taylor and Richard Burton's real-life marriage to the test. The film is adapted from the play of the same name by Edward Albee about a couple who psychologically manipulate each other and their dinner guests - another married couple - over the course of a very long, cruel night. At the end of the film, Martha and George have all but destroyed each other.

Taylor won an Oscar for her performance. Burton was nominated for an Oscar and won a BAFTA for his role. Liz and Dick did this film two years after their first marriage to each other. They got divorced in 1974 and wed again in 1975. Their second married ended in another divorce in 1976. Like Martha and George, their marriage was contentious. Some of Taylor's biographers claimed that playing Martha and George ultimately destroyed their marriage.

10. Timothy Spall and Rafe Spall - A Room With a View

Rafe and Timothy Spall in Room with a View

Who would think that Wormtail had a hot son? Timothy Spall is best known as a character actor, famous for his aforementioned role in the Harry Potter films as well as a long list of credits in period pieces. His son Rafe is known for comedies as well as playing romantic leads in period pieces. He's been in every film in Edgar Wright's Cornetto Trilogy. He's taken on the role of one of literature's greatest Byronic heroes, Charlotte Brontë's Edward Rochester from Jane Eyre. However, Spall didn't play Rochester in Jane Eyre. He played the part in an adaptation of Jean Rhys's Jane Eyre prequel novel Wide Sargasso Sea.

He also plays the passionate George Emerson in the 2007 TV movie version of A Room with a View, in which Timothy Spall played his father. A Room with a View is adapted from the E.M. Forster book and follows Lucy Honeychurch, who leaves England to take a trip to Florence. She falls in love with George, who's staying at the same hotel with his unorthodox father. She tries to deny her feelings for him because he's from an inferior social class.

9. Will Smith and Willow Smith - I Am Legend

Will Smith as Robert Neville and Willow Smith as Marley Neville in I Am Legend

Will Smith and daughter Willow have only shared the screen once, when they played father and daughter in I Am Legend (2007). Will Smith plays U.S. Army virologist Robert Neville, who is the last person in New York after a plague killed everyone. He must work to find a cure while battling mutants. Willow Smith plays his young daughter in flashbacks. After acting with her dad, she continued acting, appearing in True Jackson, VP, Madagascar: Escape 2 Africa, and Kit Kittredge: An American Girl, before transitioning to a music career. In 2010, her soon-to-be-famous single "Whip My Hair" dropped.

At the I Am Legend press junket, Will Smith discussed working with his daughter, saying "You kind of don’t work with Willow, you work for Willow. ... She just loves it." On shooting in freezing temperatures, Will Smith said, "Willow is out there, she has her stuff on, and she’s cold. She is getting a little irritable. She looks at me and says, ‘Daddy, I don’t care how low it goes, I’m going to finish.’ I was like, ‘Wow!’ I said, ‘That’s good baby, because Daddy is leaving if it go any lower than that one.’"

8. Will Smith and Jaden Smith - The Pursuit of Happyness

Chris and his son cross the street in Pursuit of Happyness

Will Smith's son Jaden first played his dad's onscreen son in The Pursuit of Happyness (2006). The film tells the true story of entrepreneur Chris Gardner and the year he and his young son (Jaden Smith) were homeless. The Pursuit of Happyness was Jaden's first film. Before that, he appeared on the TV show All of Us.

Jaden Smith is still acting to this day. In 2013, he would play his father's son again in After Earth, a sci-fi film that finds Cypher (Will Smith) and Kitai (Jaden Smith) stranded on Earth a millenium after it as been evacuated by humans.

Jaden's other credits include The Day the Earth Stood Still and The Get Down. He has a role in the upcoming film Life in a Year. Jaden is also a rapper: he collaborated with Justin Bieber on the 20120 song "Never Say Never."

At the I Am Legend press junket, Will Smith explained that Jaden inspired Willow to start acting, saying "After The Pursuit of Happyness and she saw what Jaden did, she thought, ‘I want that.’"

7. Angelina Jolie and Jon Voight - Lara Croft: Tomb Raider

Angelina Jolie as Lara Croft and Jon Voight as Lord Richard Croft in Lara Croft Tomb Raider

Angelina Jolie's parents were both actors, so her choice of career isn't exactly surprising. Her father is Jon Voight, who has a long resume that includes Mission: Impossible, Transformers, Ray Donovan, and more. Her mother is Marcheline Bertrand, who appeared in a few films.

Tomb Raider was the second time Jolie played Voight's daughter. The first was Lookin' to Get Out in 1982. At seven years old, this was Jolie's acting debut. Bertrand was also in the film, though not as Jolie's mother. The film follows Alex Kovac (Voight), who loses money gambling with gangsters and tries to win big at a casino so her can pay it back. Their next collaboration, Lara Croft: Tomb Raider, was based on the video game Tomb Raider and followed Croft as she tries to steal ancient artifacts from the Illuminati. Voight plays her dad Lord Richard Croft.

Besides Tomb Raider, Jolie is known for films like Mr. & Mrs. SmithMaleficent, and Girl, Interrupted.

6. Sylvester Stallone and Sage Stallone - Rocky V

Sylvester Stallone as Rocky and Sage Stallone as Rocky Jr. in Rocky V

In the fifth Rocky film, Sylvester Stallone's son Sage plays Rocky and Adrian's son, Robert "Rocky" Balboa, Jr. It was his first onscreen role. The Rocky franchise had trouble holding down an actor to play Robert: a different actor has played him in every Rocky film he appears in. Sage's brother Seargeoh Stallone took on the role in Rocky II (1979) when he was a baby. That was Seargeoh's first and only acting job.

Sylvester and Sage also appeared in the film Daylight (1996) together, thought not as parent and child. Sylvester Stallone led the film as Kit Latura, an EMS chief who must save a group of people trapped in New York's Holland Tunnel after a cave-in. Sage continued acting until 2010, two years before his death from coronary artery disease.

Besides the Rocky franchise, Sylvester Stallone is known for Rambo and The Expendables and has a role in the forthcoming Guardians of the Galaxy Vol. 2.

5. Gwyneth Paltrow and Blythe Danner - Sylvia

Gwyneth Paltrow as Sylvia Plath and Blythe Danner as Aurelia Plath in Sylvia

Both of Gwyneth Paltrow's parents are in the film world: her mother is the actress Blythe Danner and her late father was the producer and director Bruce Paltrow. Blythe Danner is best known for Meet the Parents1776, and Will & Grace. Additionally, Paltrow's younger brother Jake is a director and screenwriter.

Paltrow made her acting debut in the TV movie High (1989), directed by her father. Gwyneth Paltrow and Blythe Danner have only acted with each other on screen twice. The first time was in the TV miniseries Cruel Doubt in 1992, in one of Paltrow's first acting roles. The next time was in 2003, when Paltrow played Sylvia Plath in this 2003 movie about the relationship between Plath and Ted Hughes, and Blythe Danner played Plath's mother, Aurelia.

Among Gwyneth Paltrow's most famous films are Shakespeare in LoveSliding DoorsEmmaThe Royal Tenenbaums, and the Iron Man movies.

4. Mamie Gummer and Meryl Streep - Heartburn

Meryl Streep and Jack Nicholson with a baby in Heartburn

Meryl Streep, the greatest actor of our generation, has two daughters who are also performers: Mamie and Grace Gummer. But only Mamie has played Streep's daughter on screen: first in Heartburn (1986) and again in Ricki and the Flash (2015).

Heartburn was a Nora Ephron-penned adaptation of her autobiographical novel of the same name. It fictionalizes the story of how Ephron's husband, journalist Carl Bernstein, cheated on her while she was pregnant with their second child. Streep played the Ephron character, Rachel Samstat, and Gummer, who was just a toddler at the time, played her daughter Annie. It was Gummer's first onscreen role, and she was credited as "Natalie Stern" to avoid press scrutiny.

29 years later, she played her mom's onscreen daughter again in Ricki and the Flash. Incidentally, although they didn't play mother and daughter in Evening (2007), Gummer played the younger version of Streep's character. In addition to these films, Gummer is known for her recurring role on The Good Wife.

3. Phyllida Law and Emma Thompson - The Winter Guest

Phyllida Law and Emma Thompson in The Winter Guest

Emma Thompson was born to actor parents. Her mom, Phyllida Law, has been in movies including Much Ado About Nothing and The Time Machine. Her dad, actor Eric Thompson, is best known for narrating the children's show The Magic Roundabout.

Law and Thompson play mother and daughter in the 1997 film The Winter Guest. In The Winter Guest, Emma Thompson plays Frances, a grieving widow who wants to move from Scotland to Australia with her teenage son Alex after the death of her husband, but reconsiders when her elderly mother comes to visit.

Law also played Thompson's mother in the 1994 BBC TV movie The Blue Boy. Here's the story: Joe is cheating on his wife Marie (Thompson). While they're staying at the hotel Joe uses for his liaisons, Marie becomes obsessed with a local ghost story. The two have done other films together, including Much Ado About Nothing. Law also made uncredited appearances in Junior and Judas Kiss, two films that her daughter was in.

2. Leslie Mann, Iris Apatow, Maude Apatow - Knocked Up

Leslie Mann, Iris Apatow, Maude Apatow in Knocked Up

Leslie Mann and Judd Apatow's daughters Maude and Iris made their acting debuts when they were young, playing their mom's onscreen daughters in the Judd Apatow-directed film Knocked Up, as well as the sequel, This is 40. They also played Mann's kids in another Apatow film, Funny People.

Both have continued acting. Iris has a role on the Netflix show Love, which Apatow co-created with Paul Rust and Leslie Arfin. She also joined the cast of 2016's Sausage Party, working with frequent Apatow collaborators like Seth Rogen and James Franco. Maude was in three episodes of Girls, which Apatow produces and writes for.

Maude is taking her career beyond Apatow-esque projects. She has two upcoming roles, one in the upcoming drama The House of Tomorrow and the other in the thriller Assassination Nation.

Judd Apatow spoke to The Hollywood Reporter about working with his kids on This Is 40. "They're not scared that cameras are around," he says. "They get sucked into what their real problems are with each other. Like, they're so annoyed with each other that they're not distracted by the fact that they're shooting a movie."

1. Tom Cruise and Nicole Kidman - Eyes Wide Shut

Tom Cruise kisses Nicole Kidman's ear in Eyes Wide Shut

Tom Cruise and Nicole Kidman got married in 1990. In 1999, they played a married couple in Stanley Kubrick's erotic thriller Eyes Wide Shut.

When Dr. William Harford (Cruise) finds out that his wife Alice (Kidman) almost had an affair, he embarks on a night-long sexual odyssey, which includes kissing a prostitute and going to a sex masquerade. Kubrick is an intense perfectionist, and the film broke the Guinness World Record for the longest continual film shoot at 15 months, which caused strain on everyone involved.

Cruise and Kidman were divorced in 2001. Although there was speculate that this film led to their divorce, Kidman denied this in an articles she penned for The Hollywood Reporter in 2012. She explained, "People thought that making the film was the beginning of the end of my marriage, but I don't really think it was. Tom and I were close then... Stanley wanted to use our marriage as a supposed reality. That was Stanley: He used the movie as provocation, pretending it was our sex life...but obviously it wasn't us." They also played a couple, though not a married one, in two more films: Days of Thunder (1990) and Far and Away (1992).

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Did you realize these actors were related? Sound off in the comments.