Megan Fox and Shia LaBeouf's Hook-Up

Yes, it's true.

In an instantly viral Details interview, Shia LaBeouf spoke at length about a supposed onset fling with Megan Fox, his former costar in the first two Transformers flicks.

PHOTOS: Megan's incredible body over the years

"Yes, Megan and Shia hooked up," a set source confirms to Us Weekly. In his Details chat, LaBeouf, 25, sputtered when asked if Fox was then involved with her now-husband Brian Austin Green during their tryst (he repeated "I don't know" 12 times).

But the kissing costars are in the clear, the source says. "It was when Megan and Brian broke up," the source explains. "They had a 10-month break before getting back together." (Indeed, Fox and Green, 36, did have a break of nearly a year before reuniting and eventually tying the knot in June 2010.)

"[Shia and Megan] bonded while filming," the source explains of the epic shoot, which was worsened by director Michael Bay's rumored temper. "Believe me, that was an unhappy set. I think they were drawn together because it was so ugly working on that film."
Although Bay has said that Fox was fired (at Steven Spielberg's demand) from the flicks for public comments she made about him, "she was never fired," the source insists. "She said enough was enough and quit."

Shia LaBeouf: Megan Fox's "S*** Talking" Got Her Fired

When Fox, 25, left the mega-successful Transformers franchise last year -- replaced by Rosie Huntington-Whiteley for Transformers: Dark of the Moon -- everyone involved with the project remained mum.

But now, with the new flick set for theaters next month, some of the major players are speaking up to GQ about the fracas.
"She was there for rehearsals," Ehren Kruger, the series' screenwriter, tells of Fox. "But she seemed like an actress who didn't want to be a part of it. She was saying she wanted to, but she wasn't acting like it."

Fox famously complained to British mag Wonderland that director Michael Bay "wants to be like Hitler on his sets, and he is. So he's a nightmare to work for."

Explains Bay: "She was in a different world, on her BlackBerry. You gotta stay focused. And you know, the Hitler thing."

Even executive producer Steven Spielberg got wind of Fox's inflammatory comments. "Steven [Spielberg] said, 'Fire her right now,'" Bay reveals to GQ.

"Criticism is one thing," star Shia LaBeouf reasons. "Then there's public name-calling, which turns into high school bashing. Which you can't do. She started s***-talking our captain."

Bay insists he "wasn't hurt" by Fox's snipe. "Because I know that's just Megan. Megan loves to get a response. And she does it in kind of the wrong way. I'm sorry, Megan. I'm sorry I made you work twelve hours. I'm sorry that I'm making you show up on time. Movies are not always warm and fuzzy."

Fox even sent her own white flag -- a text message -- to Bay three months ago, he says. "She said, 'I hope you're doing well.'...When you're days and months on a set, it's like a family. You say rude things and you make up."