HOW IT STARTED: People on the set of Justin's new movie 'Black Snake Moan' noticed that Timberlake and co-star Christina Ricci were "bonding" in a big way.

HOW IT SPREAD: Actually, Cameron herself helped spread the rumor. She complained to friends that Christina was hyper-aggressive with Justin. We're told Diaz squarely confronted Timberlake about his relationship with Ricci at his 25th birthday bash at Pure nightclub in Las Vegas.

THE TMZ LOWDOWN: TMZ has learned that during the filming of 'Black Snake Moan' Christina tried to bond with Justin's mom, Lynn Harless, and that set Cameron off. Christina and Lynn went shopping together and even cooked meals together.

Cameron and Justin have been together for three years and so far there has been no engagement announcement. She's 33. He's 25. The buzz is that Cameron wants resolution one way or the other but Justin doesn't want to commit.

So, are Cameron and Justin headed for splitsville?
Source: TMZ