PARIS HILTON AND BENJI MADDEN ???

Paris Hilton and Benji Madden are dating.

"They're really into each other. It's serious," a mutual friend of the pair's tells us.

Things are so serious that, sources tell us, the Good Charlotte rocker accompanied Hilton on a work trip to St. Louis this weekend, where she went to promote her new fragrance.

Maybe Benji will even accompany Paris to nightclub Home, where she is scheduled to DJ on Saturday night.