"The Big Bang Theory" actors Kaley Cuoco and Johnny Galecki recently opened up about their on-set romance to journalist Jessica Randloff for her upcoming book, "The Big Bang Theory: The Definitive, Inside Story of the Epic Hit Series," where excerpts were recently published in Vanity Fair.

The couple met on set of "The Big Bang Theory" where they dated for two years before they called a quits in 2009. As of today, Galecki appears to be publicly single and Cuoco is currently dating "Ozark" star Tom Pelphrey. Although the two have moved on, they remain close friends and didn't hold back on gushing about each other when asked about their on-set romance by Randloff.

The pair played the show's central love interests, Penny and Leonard, and spoke about their strong chemistry from day one on set. “I think a lot of what made Leonard and Penny work so well was my relationship with Johnny off camera, which turned into such sarcastic banter that bled into Penny and Leonard,” Cuoco told Radloff. “Johnny and I’s relationship, in a way, was mimicking Penny and Leonard. They were always giving each other sh*t, and Johnny and I have a similar relationship — which you do after years of being together. We’ve always had each other’s backs, and you can’t lose that. And I do think it happened on-screen. It made our relationship funny and endearing.”

They also recounted how they chose to keep their relationship a secret from the cast and crew, noting that it was a bit tricky. Galecki shared a memory where the shows creator, Chuck Lorre, caught them kissing. "There was one time Chuck busted us hiding behind a car in the parking lot,” Galecki said. “It was after a show when we went outside, and we saw Chuck walk solo out of the stage. We were by some cars, and we ducked down, like kids hiding from their parents!”