Kaley Cuoco and Johnny Galecki found love with one another way before their former “Big Bang Theory” characters Penny and Leonard Hofstadter did.

In an excerpt from The Big Bang Theory: The Definitive, Inside Story, published by Vanity Fair on Monday, the exes opened up about the early stages of their real-life romance and why they decided to keep it a secret.

“I had a very big crush on Johnny early on,” Cuoco, 36, confessed. “There was chemistry and we were crushing on each other. That was the whole first season until we actually got together for real.”

The actors’ first kiss also served as their characters’ first kiss in season 1, episode 6 but it wasn’t until the 14th episode, “The Nerdvana Annihilation”, where the two “fell a little in love in that elevator shaft,” Cuoco said, referring to Penny’s dream sequence when Leonard saves her from the broken elevator.

“I think that was a massive turning point [in our relationship],” Galecki, 47, agreed. He eventually asked Cuoco out for a drink and they “kissed at the bar!” the actress recalled.

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THE BIG BANG THEORY, Johnny Galecki, Kaley Cuoco, ‘The Loobenfeld Decay’, (Season 1, episode 10, aired March 24, 2008)
THE BIG BANG THEORY, Johnny Galecki, Kaley Cuoco, ‘The Loobenfeld Decay’, (Season 1, episode 10, aired March 24, 2008) — Photo: CP Images/ Cliff Lipson / ©CBS / courtesy Everett Collection

From that point on, the couple decided to keep their relationship from the public eye, including the rest of their cast and crew.

“When we were dating, Johnny was very worried about ruining the fans’ outlook on Leonard and Penny, because they weren’t even dating yet at that point in the series,” Cuoco said. “He was so cerebral, and I’m like, ‘What?! Who f**kin’ cares?! They’re gonna be fine!’”

The “Flight Attendant” star eventually came around to Galecki’s point of view — he was concerned their romance would “complicate” fans’ perceptions of their characters.

“He was very protective of what the fans would think, because we wanted them to want Leonard and Penny together so badly, that if they saw us together in real life, it could ruin the fantasy,” she explained.

“And if we broke up, how would that affect their acceptance of the characters?” Galecki added. “At that point in my life, that felt embarrassing. I would feel differently about it today. … But at that time, it was complicated for me, and we didn’t talk about it. And Kaley was really respectful of the parameters that I had about it.”

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The couple eventually came forward to their coworkers but continued to keep their relationship from the public. However, over time, hiding it from the vast majority took its toll, slowly leading to their breakup.

“I was very uncomfortable with being public about it, and I think that hurt Kaley’s feelings a little bit, and I can understand that,” the “Roseanne” alum shared, clarifying that he was never “embarrassed of her or our relationship.”

“At a certain point it felt like we were living this lie because we were going to award shows and functions and pretending like we’re not a couple, when in fact we were a very loving couple,” he added.

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Cuoco and Galecki dated from 2008 to 2010. Following their split, the former costars remained close friends.

“I adore the friends that we are,” Galecki said. “I think I might value my relationship with her more than any other previous relationship or relationship afterwards. … We just have such a bond that I appreciate so much. And I think that’s part of our great friendship.”

Although “there was some hurt there for a bit,” Cuoco said “it didn’t take us that long to go back to what we were before we were dating and be friends… We’ve been so supportive of each other ever since. We adore each other.”