Kunal Nayyar, Kaley Cuoco, Johnny Galecki, Jim Parsons, Mayim Bialik, Melissa Rauch and Simon Helberg all took the stage Thursday night, a few hours after the Big Bang series finale aired, to dish on some secrets about their time on set.
One of the most surprisingly risque of Colbert's questions came "from an anonymous member of the group, for the entire group," meaning one of the stars on stage: "Did anyone have sex in their dressing room? [Answer with a] show of hands."
The stars laughed along with the studio audience, and no one was in a hurry to admit it, although eventually Cuoco and Nayyar both pointed a finger at Galecki.
"You must have," they said nearly in unison, as Galecki bashfully raised his hand.
As the audience roared, Cuoco declared, "And that did not include me. Just FYI." Cuoco and Galecki previously dated for two years while filming the sitcom before breaking things off in 2009.
"Actually, we all just used Johnny's dressing room," Helberg quipped.
But not all the questions were as NSFW as that one. At one point, Colbert asked each cast member about their favorite guest stars.
"Judd Hirsch was a big deal for me," Galecki recalled. "We ran into him at some function and I ran up to him and I said, 'I'm such a massive fan of Taxi, and your role on that,' and I kind of tried to base the purpose of my character on the purpose of your character,' and I said, 'Do you want to play my dad?' And then I realized he might not have any idea what show I'm talking about or that I'm an actor even!"
"Mark Hamill was pretty exciting, and Bob Newhart," Bialik said. "I grew up watching Newhart, that was one of my earliest comedy inspirations."
Another question, this time submitted via Twitter by a Big Bang fan, asked about Penny's last name before she married Leonard, which was never mentioned during the show and became a running joke throughout the series' run.
"There really is no answer. She's Cher," Cuoco joked.
The actress previously told TVLine that she "kinda loves" the idea of Penny's surname staying a secret. "'Cause so many things are revealed in the last few episodes, you get a lot of satisfying moments, I'll tell you that. But that I kind of love."
"I love it too, 'cause Johnny [Galecki] always says, 'It's Hofstadter! It's Hofstadter, that's her last name,'" she said, referring to his character Leonard's last name.