Speaking to Details magazine, he said, "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.
"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... It was what it was."
The actor insists he's unaware if Fox was dating her now-husband Brian Austin Green at the time of their tryst, and the actress has so far kept quiet about the speculation.
But now her publicist has confirmed LaBeouf's revelations, telling the New York Daily News, "It is true."