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You couldn't think of a better way to shill Mila Kunis and Justin Timberlake's upcoming movie Friends with Benefits, than a real-life situation where the co-stars actually turned out to be just that: friends with benefits.

That's our explanation, anyway, for rumours the screen couple has been acting like a real couple off set -- something of a no-no, considering Timberlake's relationship with fellow beautiful person Jessica Biel and Kunis's eight-year relationship with Macaulay Culkin.

But "insiders" have shot down the gossip, and as one source told Hollywood Life, "There is NOTHING romantic going on between Justin and Mila. They are just friends. Basically, they go to work and leave -- and not together, either."

Another source has a similar impression: "Justin and Mila get along like brother and sister. (Rumours that they're together) are laughable."

Brother and sister with benefits? Ick. It's not like they're trying to promote a Flowers in the Attic movie. We'd like to believe there's zero canoodling going down. Besides, as Hollywood Life reports, Culkin has made sure to spend lots of quality time on the film's Malibu set.

"Macaulay has actually been (on set) a lot; he's very friendly with Justin and vice versa," says the outlet's snitch.