Madden just broke up with fiancee Sophie Monk

Paris Hilton was spoofed by Sophie Monk in "Date Movie," but now it looks like the celebutante is replacing the actress in a real-life role: girlfriend.

Less than two weeks after Monk and Good Charlotte musician Benji Madden broke off their engagement, Madden has been seen cosying up to Hilton, report celebrity news sources.

"Yes, they are dating. It's pretty serious," a source confirms.

The new couple has been spotted together all over the country, mainly in West Hollywood and Beverly Hills, but also in St. Louis. They've been going heavy on the PDA: holding hands, kissing, cuddling and yes, even canoodling.

Hilton, 27, and Madden, 28, even grabbed a lunch with Madden's mother.

Naturally, the gossipmongers are hoping for a serious connection because if this new couple heads to the altar, then Hilton and her BFF Nicole Richie will be sisters-in-law ... eventually. Richie is planning on marrying her baby daddy, Madden's twin brother Joel. Nicole and Joel have a newborn daughter together, Harlow.

Monk, 28, is an Australian actress/model/singer who met Benji Madden on the set of a Good Charlotte video. In 2006, Monk starred in the comedy "Date Movie," in which she spoofed Paris Hilton's car-washing Carl's Jr. commercial.

Hilton's acting chops were recently put on display in the low-grossing comedy "The Hottie and the Nottie." Her other credits include "House of Wax," "Bottoms Up," "Pledge This!" and several seasons of "The Simple Life" alongside Richie.