"Everyone thinks it's wild but are so happy for them," one source told Us. "Benji always tends to fall in love easily, but this time it's for real and he landed a great girl."
Diaz's famous exes include Justin Timberlake and Alex Rodriguez. Benji Madden's twin brother, Joel Madden, is married to Nicole Richie. The brothers attended La Plata High School. Benji Madden has been linked romantically to Paris Hilton and Sophie Monk.