With Paris Hilton out in Hawaii, Kimberly Stewart is left with no one to copy. Maybe that's why she decided to hookup with Tommy Lee. The May-December couple, who met in London a few months ago, was spotted at the opening of Pink Taco in L.A. last week, Page Six reports. Kimberly left the party to meet Tommy outside when he was denied entry after the fire department shut down the event. "They threw their arms around each other and she started saying, 'Baby, baby,' before kissing and leaving," the spy says.

Wow -- if party girl Kimbo's gonna leave a party for a guy, you know it's gotta be serious!