While singer Avril Lavigne’s husband, Deryk Whibley, is on tour with his band, Sum 41, Avril isn’t sitting around waiting for him to come home. In fact, Avril’s been photographed partying her ass off in the French Riviera with none other than Paris Hilton’s and Mischa Barton’s ex-boyfriend, Brandon “Greasy Bear” Davis, oil heir and douchebag extraordinaire. The new photographs have kick-started another round of rumors about the stability of Avril and Deryk’s marriage.

While Derek Whibley was performing onstage with his band, Sum 41, his wife, Avril Lavigne, was spotted partying on the French Riviera with oil heir Brandon Davis, sparking rumors that the pair are getting closer by the day. Avril hit the scene in St. Tropez a few days after Brandon flew in on July 16.

“Brandon and Avril hang out together all of the time, but it’s unclear if Deryck is award of it,” a pal reveals. “Brandon and Avril are always careful not to be photographed together.”

Although a rep for Avril says that she and Brandon just happened to be at the same yacht party and Brandon is “just a friend,” an insider questions whether it’s really a coincidence that they were both here at the same time. In recent months, Avril and Brandon, 30, were spotted all over LA, including West Hollywood bar El Carmen, Pace restaurant, and partying at hotspot MyHouse.

But the French getaway definitely appeared to lift her spirits. Just days before, Avril, 24 and Deryck, 29, were having a more low-key time at Madeo in LA together. “She looked miserable when she was leaving,” says a witness.

[From In Touch print version, Aug. 10, 2009]

I don’t know if I believe that Avril is getting romantic with Brandon Davis. First of all, Avril pretty much looks miserable all the time, except for when she is drunk off her ass. Oil heir or no, it would definitely be a downgrade on the celeb ladder to trade her rock star hubby in for Paris and Mischa’s sloppy seconds. I think she is just looking for someone as rich and connected as she is to drink and party with while her husband’s away. And maybe a drunken roll in the hey every once in a while – if she’s willing to risk exposure to the herp! I do wonder when she finds time to do all that charity work she is always talking about in between the shots and yacht parties, don’t you?

Header photo of Avril Lavigne dancing and drinking with friends at the VIP Room nightclub in Saint Tropez on July 23rd. Photos in trucker hat taken yesterday; photos in black hat were taken on July 26th. Images thanks to Fame Pictures .