In a new, extremely candid interview with Details, Shia Labeouf admitted he hooked up with Megan Fox while shooting 'Transformers'--and now an on-set source is confirming it.

"Look, you're on the set for six months, with someone who's rooting to be attracted to you, and you're rooting to be attracted to them," Labeouf told Details in their latest issue. "I never understood the separation of work and life in that situation. But the time I spent with Megan was our own thing, and I think you can see the chemistry onscreen."

And what about Fox's relationship with her husband, Brian Austin Green? "I don't know, man. I don't know. I don't know. I don't know ... " he says, repeating 'I don't know' 12 times, in 12 different ways before finally saying, "It was what it was."

And Wednesday, an on-set source confirmed to UsMagazine.com that the two really did have a relationship. "Yes, Megan and Shia hooked up. It was when Megan and Brian broke up," the source revealed. "They had a 10-month break before getting back together."