Sources reveal exclusively to PerezHilton.com that Kelly Osbourne's purse was stolen at a GQ magazine party at the home of Frank Sinatra in LA on Saturday night.

And, friends of Osbourne's think her former friend, Lindsay Lohan, who was also at the party, stole the purse!

"Kelly is so upset and angry," says a friend of Osbourne's. "We're all almost certain that Lindsay stole the purse or threw it in a garbage bin. She thinks doing **** like that is funny!"

Osbourne - we're told - is willing to offer anyone a reward if they find her lost purse.