The couple reportedly started dating last May, and clearly the relationship quickly turned serious. The couple was recently spotted together on a trip to Miami in July after spending time with Diaz's family in Ana Maria Island, Fla.
Benji's twin brother Joel (the brothers are members of the band Good Charlotte and recently have been playing under the name The Madden Brothers) is married to Nicole Richie, who actually introduced Benji, 35, to Cameron, 42.
"I am a devoted sister-in-law," Richie said on Watch What Happens Live in July. "I'm happy for anyone who is happy, and I want everyone to be surrounded with love." Nicole Richie and Cameron Diaz as sisters-in-law? They'd make quite a dynamic (and super fashionable) duo!
Related Video: Recreate Cameron Diaz’s Beachy Waves from Our May Cover!