Shia LaBeouf and Megan Fox

Shia LaBeouf apparently loves to kiss and tell — perhaps too much.

The actor admits in the August issue of Details that he had a fling with former Transformers co-star Megan Fox and suggests she may have cheated on then-boyfriend Brian Austin Green.

Check out photos from Transformers: Dark of the Moon

"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," he says. "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 on-screen."

LaBeouf, 25, did not give any details of the romance. Asked if Fox was dating Green at the time — the couple split in 2009 before reconciling a year later and getting married — LaBeouf says, "I don't know, man. I don't know. I don't know. I don't know," repeating the phrase 12 times. "It was what it was."

Fox was replaced by Rosie Huntington-Whiteley in Transformers: Dark of the Moon, which hits theaters Wednesday. (According to Michael Bay, executive producer Steven Spielberg told him to fire her after she compared the director to Hitler.)

Michael Bay: Steven Spielberg told me to fire Megan Fox

LaBeouf, who's currently dating stylist Karolyn Pho, also reveals he once went on a date with Hilary Duff ("probably the worst date either of us have ever had") and confesses to "philandering around" with Transformers: Revenge of the Fallen co-star Isabel Lucas. The actress was dating Adrian Grenier and was in LaBeouf's truck the night of his 2008 car accident. "It was sort of disastrous," LaBeouf says. "Neither one of us, I think, were in love. Just sort of experimenting or whatever."

He reserves nicer sentiments for ex Carey Mulligan, whom he met on Wall Street: Money Never Sleeps. "I still love her," he says. "I think she's a f---ing awesome person and an incredible actress. We're still pals. I wouldn't take any of it back, and I don't think she would either. It just ran its course."