Cameron Diaz, Justin Timberlake, Christina Ricci Triangle?

While rumors swirl about an engagement between the adorable Justin Timberlake and his three-year girlfriend Cameron Diaz, a report hints that there may be trouble in paradise in the form of JT's 'Black Snake Moan' co-star Christina Ricci.

Trouble in Paradise?

Uh-oh.

A report set for press in the American tabloid Life & Style will dish this week that Cam is worried that he may be cheating with Christina.

Just to make certain she keeps her man happy, Cameron planned to make Justin's 25th birthday one to remember, the item dishes.  On Jan. 31, the couple partied at Las Vegas’ Pure nightclub - then headed for a bed in the VIP area, where Cam, 33, grabbed JT “for a long makeout session,” a witness tells the weekly.

But - the L&S love report will detail that Christina, 26, is head over heels for Justin, and Cameron is so upset, she confronted Justin and demanded to know if he was sleeping with the buxom actress, insiders say.

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One insider says Justin denied it, angrily asking Cam, “Can’t I have a friend other than you?”

Rumors that Christina is crazy about Justin surfaced when she dumped boyfriend Adam Goldberg, 35, after she filmed 'Black Snake Moan' with Justin.

Since then, the report reads,  Christina and Justin talk often on the phone.

“He calls her as much as she calls him,” says a pal of Justin’s.  “She’s causing a lot of problems for JT and Cameron.

Cue the reps:  Justin and Christina’s reps deny the story, but Cam’s rep didn’t respond to a request for comment.

--Lynda Johnson