Hilton and Madden have been photographed wearing rings with each other's initials. The 27-year-old socialite also joined her boyfriend when he toured with his rock band, Good Charlotte.
The 29-year-old Madden plays guitar, and his identical twin brother, Joel, is the lead singer.
Joel Madden has a daughter with Nicole Richie, Hilton's longtime friend and reality-TV co-star.
