Star Mag claims that after a steamy session on the dance floor during the VMA after-party at 1Oak, "It's on!" between Justin Timberlake and Rihanna!

A source tells the mag that after Justin took a Rihanna for a drive on the dance floor, the two continued the ride up in her hotel room. “They tried to keep it a secret, but Jessica found out within days,” says the snitch of JT's gf of three years. “She must be a wreck.”

Yeah, no kidding. But have you seen Jess' arms lately? Would Justin really want to piss her off?

The source goes on to say that Justin and Rihanna's hookup was not a "one night only" kind of fling.

"Rihanna and Justin have been talking and texting on the phone nonstop since the VMAs,” says the spy. “She asked him on the phone, ‘Are you still with Jessica?’ And he hinted that things were cooling off between them.”

But the last time we checked in on the longtime couple, it looked like everything was A-ok! Jessica even announced her plans to follow Justin to Tanzania to climb Kilimanjaro in the name of charity!

But the source insists that Justin and Rihanna's relationship is more than just in friends with benefits! “One time, Justin was joking about strippers. He said she needed to entertain him like that.” Says the source, adding that Rihanna took the bait and gave him an impromptu lap dance!

Justin and Rihanna may have been seen together in New York, but it could just be business rather than pleasure. After all, they don't really seem like each other's type!