Avengers: Endgame wrapped up an incredible decade's worth of Marvel character arcs this year. While it closed chapters on some of the longest-standing heroes, the Russo brothers were able to tie up these stories with a nice little bow that many fans appreciated. The actors behind these characters have also shown immense gratitude in being a part of the films, especially in regards to Chris Evans and Robert Downey Jr. who bowed after their final acts in Endgame.

The last few days on set must have been an emotional rollercoaster for those who knew their time in the MCU was coming to a close. Likewise, fans are still scouring the internet for insights into the film that is now officially dubbed the "greatest movie of all time," grossing more than $2.7 billion dollars. If you're wondering what it takes to make such an immensely successful film, take a look at these 10 facts behind the making of Avengers: Endgame.

RELATED: Avengers: Endgame: 5 Ways It's Better Than Infinity War (& 5 Ways It's Worse)

Filming Started in Late 2017

Avengers: Endgame had originally been set to debut in early May, but in true MCU fashion, that anticipated date was eventually pushed up to April 22nd, 2019. It seems like a short time frame considering that filming had just started in August of 2017. On top of that, many of the actors were filming dual Marvel films at once. Ant-Man and the Wasp (which came out in 2018) had been borrowing Paul Rudd and Evangeline Lilly from the set of Endgame, meaning the actors were filming both films at the same time. 

Likewise, Brie Larson had been dumped right into the MCU starting with Endgame, despite the fact that her solo film, Captain Marvel, came out a few months earlier. After all is said it done, Endgame wrapped up filming in just five months in January 2018. Apparently, it doesn't take that long to shoot, direct, and edit a Marvel film (or their team is just that good).

NOBODY Gets The Full Script

It's no secret that the Marvels scripts are kept under lock and key. It's hard to say when this trend started, but suffice it to say that Tom Holland's (Spider-Man) incessant spoiler spills probably had something to do with it.

That being said, not a single person, cast or crew, were given access to the full script. The exception was Robert Downey Jr., who was given permission to read the script front to back. This probably had something to do with the fact that the Russo brothers had already informed Downey of Tony Stark's own inevitable endgame, so he probably earned rights to the full script in order to sign off on Iron Man's farewell.

I Love You 3000

Avengers Endgame Iron Man Tony Stark Death Robert Downey Jr

One of the most quoted lines from the film comes from Tony Starks daughter, Morgan Stark (Alexandra Rachael Rabe). Their father-daughter mantra of "I love you 3,000" became all the more meaningful when Iron Man snaps his fingers to put a final end to Thanos' endgame.

The fact that this quote stems from Robery Downey Jr's own daughters makes the line all the more enjoyable. Apparently, Downey told the Russo brothers that one of his children told him "I love you 3,000" and they thought it was so adorable, they immediately penned it into the script.

RELATED: Avengers: Endgame: 10 Times A Whole New Timeline Was Created During Time Heist

Natalie Portman Didn't Film New Scenes

Natalie Portman as Jane Foster in Thor

One of the biggest surprises that came from Endgame is the reappearance of Natalie Portman as Jane Foster. Her character hasn't been seen in the MCU since 2013's Thor: Dark World after a seemingly messy break from the Marvel franchise. Everyone's curiosity was satiated after it was revealed the Portman didn't actually film any new scenes for Endgame (save a few voice-over lines). The editors simply used old footage of her from previous Thor films.

Now that audiences know that Portman will be playing an even bigger role in the MCU as the acclaimed comic version of female Thor, it's safe to say that Portman's friction with Marvel has officially fizzled out.

Inspiration Behind the Endgame Autograph Credits

With the ferocious (albeit, heartbreaking) Endgame finale, came a new credits sign off. Marvel is notorious for its after-credit scenes, but in light of the events of the film, the Russo's decided to negate this experience from Endgame. Instead, the final scene cuts to its atypical list of the main cast, except this time, names like Scarlett Johansson and Chris Hemsworth were partnered with the actor's autograph.

This is a touching move on the MCU's part, though this attribution is not unique. The Russo's drew inspiration for these end credits from the 1991 film, Star Trek VI: The Undiscovered Country, which also uses autographs as a tribute to the actors.

Joe Russo's Daughters Are In Endgame

Mark Ruffalo as Professor Hulk in Avengers Endgame

The children of Joe Russo had a unique opportunity to try their hand at acting. His daughter, Ava Russo, plays the role of Hawkeye's daughter, Lila Barton in the opening scene next to Jeremy Renner.

Russo's other daughter, Lia Russo, is credited with her own name for her scene with the Hulk. She's the girl who comes up with the two light-haired boys to ask (rather enthusiastically) for the Hulk's autograph.

The Fate Of Captain America and Iron Man

Tony and Steve prepare to time travel in Avengers: Endgame

The fate of Iron Man and Captain America was, unfortunately, a long time coming. The decision to remove these two pivotal characters from the franchise was decided by the creatives of Marvel in the early processes of Avengers: Infinity War. Infinity War began filming in January 2017, but the fate of these two heroes had already been decided by then,

Which means that Robert Downey Jr. and Chris Evans may have known about their character's end for the past 2-3 years.

RELATED: 10 Facts About The Avengers That Make Endgame More Heartbreaking

RDJ Hid Snacks On Set

Robert Downey Jr as Tony Stark in Iron Man 2

There are a few scenes in which Tony Stark unabashedly starts munching on snacks during the Avenger's meetings. Apparently. Downey is known for hiding his own snacks throughout the set, so he would randomly pick them up, despite if the cameras were rolling. The scenes where Tony offers his snacks to his fellow Avengers had not been written into the script at all. They were just a happy accident thanks to Downey's improvisation.

Captain Marvel Nods

Captain Marvel arrives on the battlefield in Avengers Endgame

Captain Marvel came out just one month before Endgame, so audiences were quick to notice Brie Larson's massive costume change. The Avenger's even point out her new short pixie cut in the film, but her new armor is also vastly more pigmented than the one seen in her solo film. This darker armor is derived from her predecessor in the comics, Captain Mar-Vell, who's comic version sports a dark chest piece and shoulder pads. The short hair comes directly from Captain Marvel's more modern comic appearances in which she wears a bodysuit with a red sash.

Another fun nod happens between Carol and Rhodey. In the comics, these two form a romantic relationship. So in Endgame, when Carol tells Rhodey to be careful, comic fans were quick to make a connection. Hopefully this relationship will develop further along in the MCU with Rhodey's new role as Captain America.

There's A Lot of VFX

Ant-Man and Wasp prepare the quantum tunnel.

It's pretty obvious that there is a ton of technical effort behind the making of Endgame. As awesome as it would be if Thano's monstrous purple look was all effects makeup, that simply isn't the case. The MCU definitely had the budget, so a lot of what you see in Endgame is with the help of VFX. VFX is simply manipulated imagery that high-budget films like Endgame have the pleasure of using in order to make things like Iron Man's suit look more realistic.

Surprisingly, though, Marvel used VFX on more than just the challenging costume concepts. Tony's massive weight loss is made with special effects imagery and so is Ant-Man's entire suit. In fact, Paul Rudd doesn't wear a suit at all in Endgame. It's all VFX.

NEXT: The 10 Best BTS Photos From The Making Of Avengers: Endgame