LeBeouf hints that his relationship with Fox, who was replaced for the third installment of the Transformers saga by British actress Rosie Huntington-Whiteley, went from professional to physical while filming the action franchise.
"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 tells Details magazine. "I never understood the separation of work and life in that situation. But the time I spent with Megan was our own thing."
He adds: "I think you can see the chemistry onscreen."
So was Fox, who married Brian Austin Green last summer after an on-and-off relationship since 2004, a single woman at the time? "I don't know," LaBeouf, 25, says. "It was what it was."
A rep for Fox had no comment about the story.
Fox wasn't the only costar that LaBeouf spoke about to Details. His Transformers: Revenge of the Fallen costar Isabel Lucas, who was in his truck when it flipped in 2008, was also mentioned.
The costars had been "philandering around" the night of the accident, although she was dating Entourage's Adrien Grenier at the time, he says, but "it was sort of disastrous."
"Neither one of us, I think, were in love," he said. "Just sort of experimenting or whatever."