Suddenly Inseparable: Paris Hilton & Benji Madden

Less than two weeks after Benji Madden split from fiancée Sophie Monk, the rocker is stepping out with another blonde bombshell. The new woman in his life? None other than Paris Hilton.

"Yes, they are dating. It's pretty serious," a source confirms of the couple, who have been spotted together all over town – make that all over the country! In just the past few days, they have partied at Home nightclub in suburban St. Louis, shopped (while holding hands) at Hollywood's Fred Segal, and even grabbed lunch with Madden's mom.

On Sunday night, the two hit the Polo Lounge at the Beverly Hills Hotel, where they cuddled in a massive booth and engaged in an intimate conversation.

And the Madden brothers posted on their Web site a group picture that included Hilton. They called it a "nice little family photo" and described her as the "wonderful Paris."

The apparent love connection is certainly convenient: His twin brother, Joel, dates Hilton's B.F.F., Nicole Richie.

Via people.com