The Big Bang Theory co-star Johnny Galecki opened up about the two-year relationship he and actress and co-star Kaley Cuoco revealed in 2010, which they kept silent to the show and each other.

"We are dear friends, still. Kaley's not just an ex, she's part of my life," Galecki shared Watch! December issue.

"Mooks - I'm not sure why but we have acquired this as a nickname for each other - and I have a very special relationship," Kaley. "We are two of the few who had an intimate relationship and came out of it as even closer friends. We have been on an amazing ride together with Big Band and both know how lucky we are. He will always have a huge chuck of my heart and continue to be my partner in crime."

Galecki said that they "just don't like to speak about it" because they don't want people to feel some kind of conflict with people's acceptance on Leonard and Penny characters.

"I get the curiosity but I don't want to distract from the story," he added. "I think every great show has that dynamic, it's a love story and that's the thing that attracted me to the part, that inspired me to ask if I could play Leonard."

Galecki and Cuoco have starred in the CBS comedy together since 2007. In 2010, Kaley opened up about their relationship, after three years of show and two of dating.