Rihanna, Ryan Phillippe Have Been Hooking Up for Months!

 John Shearer/WireImage.com; Joe Scarnici/Getty Images

Rihanna's got a steamy new collaboration! Though one source told Us Weekly the singer, 23, appeared to blow off Ryan Phillippe, 36, at a Gucci/Roc Nation brunch in L.A. on Feb. 12, a second insider says it was actually just the opposite — and that the two had a sleepover that very night!

PHOTOS: Undercover lovers

"She thinks he's hot," says the source. "They totally had sex. And it wasn't even the first time!"

"They initially hooked up when things were strained with [Rihanna's ex] Matt Kemp back in early December," says a Rihanna source. Phillippe (whose three-month, nonexclusive romance with Amanda Seyfried recently fizzled) and Rihanna then reconnected at Bing's Two Kings charity event Feb. 19 — though again, they played it cool.

"There was no PDA," says an attendee of the Los Angeles party. The next day, he went to her 23rd birthday party at a Beverly Hills home. Says an onlooker, "They hung out a bit, but were discreet. It is still very casual." Sums up another source, "Clearly they're keeping it on the downlow!"

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