When a group is as large as the main cast in The Big Bang Theory, there are always going to be juicy revelations. Howard, Sheldon, Stuart, Bernadette, Raj, Penny, Amy, and Leonard made for a quirky circle of friends whose backstory and life decisions were usually presented in the form of secrets that were later revealed.

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The characters would generally be secretive about embarrassing facts about their pasts, which others would humorously find out one way or another. In the 12 years that The Big Bang Theory was on-air, some of these secrets brought on quotes that made fans cry and were more notable than others, and it's worth remembering some of the series' biggest.

Updated on May 5, 2022, by Lynn Gibbs: As close as the characters on The Big Bang Theory are, they didn't always feel comfortable sharing embarrassing, exciting, or dark information. Sheldon and Leonard are perfect examples of friends who lived and worked together but didn't always share things with one another. Even when these characters found girlfriends and wives, secrets were still kept. These secrets may have seemed small to viewers but they were big to the characters. 

Leonard: His Secret Bank Account

Leonard and Penny argue at the cabin in The Big Bang Theory

Leonard and Penny have done some sweet things for each other over the years, but they came head to head when she found out he kept a secret from her.

In 'The Big Bear Precipitation,' Sheldon and Amy went away to Big Bear for the weekend with Leonard and Penny. Due to the rain, the foursome stayed inside by the fire and played a game. Through the game, Penny found out that Leonard kept a separate banking account that she didn't know about. Because of Penny's rough past with money and debt, Leonard kept this account a secret. When she found out, she was bothered that he would keep something like that from her now that they were married.

Sheldon & Leonard: A Late DVD And An Itchy Sweater

Leonard wearing the itchy red sweater and talking to Sheldon on The-Big-Bang-Theory

Leonard and Sheldon have one of the best friendships in TBBT. After living with each other for over a decade, they understood and respected each other on a different level that Penny and Amy would never understand.

However, even best friends and roommates keep things from each other. In one episode, Leonard revealed one of his best-kept secrets: he never returned a rented DVD that was charged to Sheldon's account years prior. Sheldon would typically be disgusted by this news and panic at the thought of being a delinquent. But as viewers found out, Sheldon also had a secret... He knew all about Leonard's late notice and returned the DVD for him.

Sheldon: His Private Storage Unit

Sheldon's storage closet on TBBT

The closer Sheldon and Amy became, the more open they were with one another. And while viewers (and Amy) thought they knew all there was to know about Sheldon, 'The Solder Excursion Diversion' proved otherwise.

Sheldon took Amy to an unidentifiable building and led her into one of the rooms. What hid inside was everything Sheldon had ever owned. From toothbrushes to clothing, Sheldon's biggest secret was that he wasn't as minimal as he led on. He was a man of science but had an attachment to the objects in his life. Sheldon was embarrassed to show Amy his secret but it made them grow as a couple.

The Guys: Howard Getting The Mars Rover Stuck In A Ditch

Howard looks embarrassed in The Big Bang Theory

The whole gang was in on the secret of how the Mars Rover was stuck in a ditch, as Howard accidentally got it there when nonsensically attempting to impress a date. The group proceeded to wipe all the records that showed Howard’s use of the Mars Rover — a secret that they held for years.

Sheldon ended up accidentally revealing it to an investigator from the FBI during a rant. This was a huge secret, mainly because it had legal ramifications, and it caused an estrangement between him and Howard for some time until Sheldon gave his spot on the couch to him in apology. It was one of the few times Howard and Sheldon found common ground

Leonard: Kissing Another Woman While In A Relationship With Penny

Penny and Leonard arguing on bed after Vegas wedding

At the end of season 6, Leonard went to the North Sea on a research expedition where he had a great time partying with other scientists. Two years later, in the season 8 finale, just before eloping with Penny, he admitted that he had harbored secret guilt of kissing another woman on the expedition. This admission made things take a turn in Penny and Leonard's relationship timeline.

This information went uncovered for years until he broke his secret, as he didn’t want there to be any between him and Penny before they got married. While the story itself wasn't popular with fans, and Penny's anger was justified, she ultimately appreciated Leonard being honest.

Bernadette: Her First Pregnancy

Bernadette and Howard save a bunny on TBBT

Bernadette had told Howard she had no intentions of being a mother, as raising her younger siblings had been a task she never enjoyed. This news took a toll on Howard and Bernadette's relationship. Fast forward, this made her onscreen reveal of pregnancy a bombshell, especially because she didn’t immediately tell Howard, choosing to keep it a secret for some time until the right moment.

As it turned out, Bernadette was right to have some reservations, as the news freaked Howard out, and he became worried that he didn’t have enough money to provide for his future child. The secret was also notable for the fact that it brought a change of character in Bernadette, as she grew to love the idea of being a mother.

Raj: His Family's Enormous Wealth

Raj and Howard on a date with Emily on The Big Bang Theory

Raj kept his family's immense wealth a secret for years to keep up his image of being a sympathetic personality, only for things to come out when Sheldon learned the truth. Considering Howard was Raj's best friend in TBBT, Howard felt duped.

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Sheldon learned about Raj's wealth while notarizing his documents. He claimed that the Koothrapalis were “Richie Rich rich,” making Raj a secret millionaire unbeknownst to his friends. All things considered, it was pretty impressive that Raj kept this under wraps considering just how affluent his family was. 

Stuart: His Inclusion In Wil Wheaton's D&D Gang

Stuart almost gets kicked out of the apartment in The Big Bang Theory

Stuart and the gang didn't always act like friends, but when Sheldon and co. did include him, Stuart loved being a part of the action. This is why the guys were so shocked when they learned that Stuart was secretly part of Wil Wheaton’s celebrity Dungeons & Dragons group — which included Kareem Abdul-Jabbar and Willaim Shatner.

Stuart was able to keep this a secret due to Wil’s threat that he would kick Stuart out if he let anyone know. Unfortunately for him, the guys ended up finding out anyway, leading to Wil following through with his promise and giving Stuart the boot.

Howard: Hooking Up With His Cousin

Howard and Bernadette at the prom in The Big Bang Theory.

The reveal of Howard hooking up with his second cousin points to Howard’s character development on TBBT, as it showed just how desperate he once was. He kept this a secret for more than a decade until saying it out loud when under the influence of pot brownies.

As it happened, Howard had lost his virginity to his second cousin and didn’t tell anyone due to how embarrassed he was. Unfortunately for him, Leonard and Raj remembered the reveal of his secret and tormented Howard with this information for years, with his cousin even being Stuart’s date for the gang’s makeshift prom.

Amy: Her Need To Be Accepted In A Social Group

Amy Farrah Fowler in her pajamas with a laptop on her lap in The Big Bang Theory

Amy never had any specific secrets, as she relished the excitement in the lives of others. However, she gradually revealed tidbits of her life before joining the group, with secrets such as her having imaginary friends, birthday parties for herself, and the fact that she used to cry about this.

She eventually admitted that her behavior upon her debut, which was very much like Sheldon’s, had been her cover. She didn’t want to be vulnerable around others and it was easier to keep the secret. It was after she became secure with herself that Amy revealed private information about herself, like rubbing Sheldon and Penny's apartment items on her body to spread her pheromones.

The Girls: Penny's Plans To Break Up With Leonard

Penny, Bernadette, and Amy on The Big Bang Theory.

The number of speed bumps in Leonard and Penny's relationship saw her contemplate breaking up with him at the start of season 6, which she told Amy and Bernadette in confidence. The girls had a hard time keeping this secret, though, as it would mean breaking their group up as well.

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Amy had the most difficult time keeping this under wraps, eventually letting Sheldon in on the secret, which caused Penny to get angry at her. It ultimately worked out, though, as Sheldon’s request for Penny to go easy on Leonard led to her giving their relationship another chance. Sheldon's pep talk with Penny was one of the most heartwarming moments in the series. 

Penny: Her Role In Serial Ape-ist

An example of Penny's acting career on The Big Bang Theory.

Penny’s acting career saw several embarrassing roles, as it never took off and she later abandoned it altogether. However, a long-held secret of hers was a role in Serial Ape-ist, a schlocky B-movie.

Funnily enough, Penny’s belief that this was a secret turned out to be false, as Howard uncovered the movie soon after he met her. Still, she did keep the information to herself for close to a decade until she got an offer for the film’s sequel.

Sheldon: His Intention To Propose To Amy

Sheldon proposes to Amy in The Big Bang Theory

Sheldon hated keeping secrets as he considered it a burden he didn’t want. Yet, he did maintain a secret of his own, which was his intention to propose to Amy. He planned on following through with this in the season 8 finale but couldn’t when Amy broke up with him.

Interestingly enough, Sheldon didn’t reveal the secret even after that, and it was his Meemaw who divulged this information to Amy. Knowing the kind of person Sheldon was, this secret was easily the biggest one that any character kept in the series.

NEXT: 10 Ways Sheldon & Amy Are The Most Relatable Couple From The Big Bang Theory