Actors professionally ‘pretend’ every day for a living. This means it can be hard to tell if an on-screen chemistry is for real or something just put on for the cameras. The American sitcom The Big Bang Theory entered the world’s living rooms in 2007 and soon fans everywhere were graced with four nerdy friends, following their professional and personal lives. Critically and publicly acclaimed, the show has won seven Emmy Awards from 46 nominations, with millions of viewers and one spin-off series. It became a slam-dunk hit that popularized nerd culture.

Working together for 12 seasons and 279 episodes, the characters on the show spent a lot of time together in real life, becoming a close circle. Arguably, one of the most prominent relationships featured on the show lies between eccentric Sheldon Cooper and his often-frustrated roommate, Leonard Hofstadter. The chemistry, conflict, and genuine affection between these two characters were a part of what made this show such a success. The characters who grew together in love and friendship on-screen also supported each other for over a decade off-screen. Here are 15 lesser-known facts about Johnny Galecki’s and Jim Parsons’ off-screen friendship!

15 Bonding Over A Shared Role

When two people are in competition for the same role it can be awkward. Thankfully, after Galecki was offered the role of Sheldon first, he turned it down because he liked the challenge of playing straight man Leonard. If Galecki had taken on Sheldon Cooper, who knows who would have been cast to play Leonard, or if the show would have become a big hit.

14 Becoming Besties

From the very first episode, there was a spark and a respect for the talent between these two leading men. Express reported that Jim Parsons said, “I knew instantly, and I couldn’t tell you even now exactly what it was, what quality, but I know how I felt when I read with him which was very free, there was something so independent about what he was doing. I literally felt it from the very first time we read through it together, it was like ‘well this is different’” The chemistry both on and off set just grew from there.

13 Shared Sad Family Stories

Sometimes it’s sharing an experience that bonds people together. Both Jim Parsons and Johnny Galecki lost their fathers in car accidents. For Galecki, this happened when he was just 16 years old, for Parsons it happened just a couple of years before he was cast on The Big Bang Theory. Sharing this type of experience and working through it together is what can bring a friendship even closer.

12 Who Are Still Friends Now That The Show Is Over?

While everyone on the show has worked well together, naturally some are closer than others. Galecki and Parsons are going to remain friends, but there are other castmates who also mean a lot. Parsons said, “I’ll particularly miss Simon Helberg; we spend a lot of time together, we go back and forth to our dressing rooms, we’ve talked for almost 12 years now.” Galecki and Mayim Bialik first met in the 1990s when he appeared on her show Blossom as a love interest, and that friendship grew over the run of Big Bang.

11 Who Attended Who's Wedding

Celebrities need to be careful to make sure their weddings don’t become a media circus. Coincidentally, Jim Parson got married just a few days after Sheldon Cooper popped the question to Amy in season 10. While the photos of the wedding weren’t plastered everywhere, cast from the show were present. During an interview, Mayim Bialik commented that the wedding was, “stunning and beautiful” but kept her lips sealed on other details, including who else was in attendance.

10 Annoyances?

The cast of Big Bang knows that the show about lovable nerds isn’t for everyone (even though millions of viewers watched it live and continue to watch it in syndication). Vulture reported that Jim Parsons said, "People have so many choices on TV now, so no one’s asking for you to marry us. You can enjoy our show without a weekly appointment.”

9 More Than On Air Chemistry

Both Galecki and Parsons have mentioned that everyone was crying during the final episode taping. The hard work and friendship that has gone on during the run of the show will last a lifetime. While acting is in the bag for the cast, showcasing scientific knowledge over the years doesn’t come that easily. Jim Parsons often looked up terms used in his lines, online, to make sure he understood them. He also said, “I do note cards all week. And in longhand, I write out all my lines again and again and again. And on the weekends, I drill them.”

8 The Mario Lopez Bromance

Outsiders on the set can change the dynamic of things. When Mario Lopez was invited to spend some time on the set of Big Bang for Extra, not everyone was loving his interview techniques. Mayim Bialik was not a fan of the questions about her love life, and Jim Parsons wanted to leave the conversation where Lopez and Galecki ‘broed’ it up over cologne scents.

7 Changing Together Through 12 Years

With a cast that has remained consistent, with a few regular additions since the start in 2007, it’s no wonder they’re all tight. In talking about how the characters have evolved, Jim Parsons told The Hollywood Reporter, Chuck Lorre once said that watching these characters change will be like watching paint dry — you wouldn't even notice it was happening. That turned out to be both true and not true. We got to play long enough that they were allowed to change and you did notice it because at some point they were writing enough episodes, like, well we have to. They have to morph a little bit. And that made it really fun. I'm deeply satisfied with how it ended."

6 Relationship Drama?

For two years, co-stars Galecki and Cuoco dated but worked hard to keep it under the radar. Cuoco said, “It was a wonderful relationship, but we never spoke a word about it and never went anywhere together." The two didn’t let the breakup impact their professional relationship. Galecki told said, "We're dear friends, still. Kaley's not just an ex, she's a part of my life." He also noted in another interview that one of the reasons they don’t talk much about it is they don’t want it to cloud people’s opinions of the Penny and Leonard relationship.

5 What They All Agreed On For The Final Episode

While changes to the script are common, with producer Chuck Lorre saying, “20% to 30% of the script will be brand new by the time we shoot it," one of the things that everyone agreed on was the theme of the final episode. No one wanted it to involve a big move or something that would tear the group apart, because at the end of the day the show was and is still about continual friendship.

4 Salary Solidarity

A big show brings in big money for the stars. Sometimes those stars recognize that it isn’t fair for those who joined a little late. It has been reported that the original five agreed to each take a $100,000 pay cut so that money could go to later regulars on Big Bang, Mayim Bialik and Melissa Rauch. Industry insiders reported, “The move is evidence of the strong camaraderie among the key players on the show that remains primetime’s most-watched comedy.”

3 How Does Johnny Feel About Jim?

Keeping good ties with past roles is part of who Johnny Galecki is, which can be seen in his cameo returns to Roseanne (where he first gained some fame), and his relationship with Jim Parsons is no different. Because the two have worked so well together there is a good chance that they will attend a Big Bang reunion (but odds are we’ll need to wait another five to ten years for that).

2 What Does Jim Really Think Of Johnny?

Twelve years of friendship can’t be faked. Jim has supported Johnny in all of his professional and personal endeavours, as Johnny has of his. Over the years this friendship has blossomed nicely. When it comes to mementos from the show, everyone got sentimental. Parsons said of wanting to keep his time with Johnny and the gang close, "The set department was gracious enough to make us all replicas of the little placard that says 4A on the apartment. I opened that and had tears in my eyes immediately. That's been funny about closing out — it's been these little trigger moments. Like, 'I'm fine, I'm fine.' And then I'm crying."

1 Future Projects Together?

In life post-Big Bang, Parsons worked on the Boys in the Band movie and joked, “Then I'm just skydiving off a cliff and see where I land." Johnny said of his post-Bang Life (in addition to becoming a father in real life, “We're producing six TV shows, a film that John Carpenter is directing and a play. I'm going to let Leonard run his course through my bloodstream before taking on much of a big role. I might do one, two at the most, episodes of The Conners because I just can't stay away from those people!"

Sources: E Online, Showbiz Cheat Sheet, A Plus, Variety, Screen Rant

Next: Johnny Galecki Is NOT Taking A Break From Acting: 15 Things He's Been Up To Since Big Bang