The former couple began dating at the beginning of their time on the CBS sitcom - where Kaley played Penny, and Johnny played Leonard - and “fell madly for each other”, but split up two years later.
Kaley - who is now married to Karl Cook - said: “We dated really early on for almost two years. When we did the pilot, I was crushing so hard on Galecki but he had a girlfriend.
“We got together and just fell mad for each other for two years, but then we broke up. Luckily Johnny and I came out of it so brilliantly and we’re closer today than we ever were.”
Although they remained close friends, their breakup coincided with the show’s creator, Chuck Lorre, developing the on-screen romance between their characters - who eventually got married - including adding more sex scenes.
And Kaley, 34, has said she found it “sensitive” to film those scenes, because their breakup was so fresh.
The actress recalled: “When we broke up obviously it was a little sensitive for a minute, but I remember those weeks that Chuck had written these episodes where all of a sudden our characters were like sleeping together every other second.”
Looking back on it, Kaley and Johnny - who has been dating Alaina Mayer since 2018 - can both laugh off the awkward tension between them, and even think Chuck added the scenes “on purpose” just to mess with them.
Speaking to Dax Shepard on his ‘Armchair Expert’ podcast, she quipped: “Johnny and I talk about it and I think [Chuck] did that on purpose - just to f*** with us. If I was with him, I would ask him because that came out of nowhere. All of a sudden these characters were all up on each other."
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