Kaley Cuoco says she dated Johnny Galecki, her co-star on "The Big Bang Theory," but it was a secret neither of them ever spoke publicly about.

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"We dated for almost two years. It was such a huge part of my life and no one knew about it," Cuoco told CBS Watch Magazine.

"This is the first time I've ever talked about it, ever. It was a wonderful relationship, but we never spoke a word about it and never went anywhere together."

The actress said the relationship eventually caved last winter under the pressure of trying to protect themselves and their show from scrutiny.

"We couldn't do anything. It wasn't as fun as we wanted it to be," she said.

"Everyone was always asking, and we deny-deny-denied. And I'm like, 'Why am I denying this person that I love?' ... We knew we weren't destined to be together. We accepted it and said, 'Look, if we ever break up, we will be professional.' I'm so lucky it was a mutual ending and that we don't hate each other. We've seen that happen on other shows."