Kaley Cuoco and Johnny Galecki‘s chemistry was so off the charts during The Big Bang Theory that they took their on-screen romance into the real world.

The pair respectively played Penny and Leonard on the sitcom for 12 seasons, from 2007 until 2019. While their characters ultimately ended up together, Cuoco and Galecki quietly dated early in the show’s run.

“There was chemistry and we were crushing on each other. That was the whole first season until we actually got together for real,” Cuoco said in a book excerpt from The Big Bang Theory: The Definitive, Inside Story of the Epic Hit Series, shared by Vanity Fair.

The pair pointed to a scene they filmed together during that first season — one where they are close together in an elevator — as when they couldn’t deny the sparks.

“I think we fell a little in love in that elevator shaft,” The Flight Attendant star and producer said.

Galecki adds, “At that point, both she and I knew that something mutual was felt, and that it was going to be more of a distraction…to try and continue to ignore it than to actually…surrender to it.”

The duo then quietly dated from 2008 to 2010; Galecki admitted they “did consider marrying.” So why didn’t their relationship pan out?

“I think one of the things that created a chasm…was my strict policies of privacy, and Kaley being very, very open about her life,” the Roseanne alum said. “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.”

No worries, though. Cuoco said she and Galecki have remained close friends throughout the years due to the bond they formed on the show.