It ain't easy being green, at least for environmentally conscious flames Adrian Grenier, 32, and Isabel Lucas, 23, who have reportedly called it quits just weeks after the actress was involved in a car accident with her "Transformers: Revenge of the Fallen" co-star Shia LaBeouf.

"It wasn't working out," an insider blabs to People. "Adrian saw her with Shia and that was kind of it -- the crash, their hanging out. He obviously didn't appreciate it."

The mag says they split shortly after the July 27 rollover wreck, which left Lucas, whose rep confirms her single status, with bruises and LaBeouf with a smashed hand and a DUI charge.

"All that stuff that happened with Shia definitely didn't help things," a snitch adds to Us. "When Adrian saw Isabel with Shia, he knew it was time to move on and made the decision to end things. He's not upset and thinks Isabel is a really sweet girl but they're done."

But TMZ says it was actually Lucas who stuck a fork in the romance, which reportedly began a few months ago.

Word is, the Aussie actress gave the "Entourage" star the heave-ho before the crash and "he's been begging her to come back ever since."

You'll recall that Grenier and Lucas made a point to step out together shortly after the accident, a public show of togetherness seemingly designed to quell speculation over why she was riding shotgun with LaBeouf.

"She's OK," Grenier told paparazzi as he strolled with Lucas in Los Angeles. "We're good."

But neither party appears too broken up about their parting of ways.

On Monday, Isabel was photographed walking in Los Angeles with Shia, whose hand remains in a splint following extensive hand surgery.

Adrian, meanwhile, has spent the last few days cavorting with some swimsuit-clad blondes and brunettes at an L.A. beach house.