Cameron Diaz  may have found a new boyfriend. The actress hit the gym last Friday with Good Charlotte guitarist (and Nicole Richie 's brother-in-law) Benji Madden, sparking rumors that the two have started dating. The two certainly have been spending a lot of time together, as their gym trip came the day after they both attended an A-list book party in LA with Nicole; Benji's brother, Joel Madden ; and Cameron's pal, Gwyneth Paltrow . A source said that Benji has been spending a lot of time at Cameron's home  and that the actress "seems very happy" with the musician, adding, "He is the nicest guy and treats her like a lady." This isn't Benji's first time getting involved with a famous woman, as he has previously dated Australian starlet Sophie Monk, Paris Hilton , and Holly Madison. He was also recently linked with Miley Cyrus . Cameron, for her part, also has a history with musicians, having dated Justin Timberlake  from 2003 to 2006. The two were so close that they have even remained close friends  after they split.