Pregnant Kaley Cuoco and her former co-star Johnny Galecki have revealed how they kept their off-screen romance a secret from The Big Bang Theory cast and crew.
The pair, who dated between 2008 and 2010, opened up about how they initially kept their budding relationship hidden from everyone and it all came down to sneaking into each other's room in the middle of the night.
Galecki and Cuoco - who is now expecting her first child with partner T om Pelphrey - said they decided to keep their romance under wraps during a group trip to Comic Con.
Cuoco told Us Weekly : "We all had different hotel rooms at Comic-Con. There were two giant buildings for this one hotel and Johnny and I weren't even in the same building.
"So we were like little mice in the night, running back and forth to each other's rooms, trying not to be noticed. I mean, who did we think we were?"
Galecki added: "So we would all be in the hotel lobby... and Kaley and I would give each other a hug and pretend to say good night, and go our separate ways."
Cuoco eventually told the show's creator, Chuck Lorre, of their romance when she was trying to make small talk.
She told the story in their new book, The Big Bang Theory: The Definitive, Inside Story of the Epic Hit Series.
Cuoco said: "This is charming looking back, but I was on a shuttle bus with the cast and I was sitting next to Kaley trying to strike up a conversation.
"The best I could come up with was, 'So ... what's going on with you? You got a fella? You seeing anybody?' Like, I'm her dad or something.
"And she starts giggling and says, 'Oh my God, you don't know?' And I said, 'I don't know what? What don't I know?' And she says, 'I'm seeing Johnny."
The pair dated for two years and things ended in 2010 on good terms.
Cuoco revealed that their relationship ended as it ran its course, explaining they 'ran out of things to talk about' as they worked together and spent most of their time together.
There was 'no foul play' when it came to the reason for breaking up.
Although there was 'some hurt there for a bit', it wasn't long before they returned to being close friends.
Galecki has a one-year-old son, Avery, with his ex-girlfriend Alaina Meyer and earlier this week Cuoco announced she was expecting a baby girl with boyfriend Tom Pelphrey.
She met Tom at the Ozark premiere on April 21, 2022, and the rest was history.
