"It's very new" and they're "just hanging out," a source tells Us of Diaz, 41, and Madden, 35. The pair have only been seeing each for the past several weeks.
As for how they met? Looks like the Good Charlotte singer has his sister-in-law Nicole Richie to thank! "Nicole thought they'd click," the source adds. (Richie has been married to Benji's brother, Joel Madden, since December 2010. They're parents to daughter Harlow, 6, and son Sparrow, 4.)
Indeed, Diaz and Richie appear to be close friends. Last month, the women were photographed enjoying a hike with each other at Coldwater Canyon Park in L.A. On May 15, they posed together while attending the launch of author Vicky Vlachonis' book, The Body Doesn't Lie.
Madden is the first high-profile relationship Diaz has had since splitting from New York Yankees third baseman Alex Rodriguez back in September 2011. Her other exes include Justin Timberlake, and Dallas Buyers Club Oscar winner and 30 Seconds to Mars rocker Jared Leto. (She recently revealed during an appearance on Watch What Happens Live that she's also "been with a lady.") Madden was previously linked to Paris Hilton.
X17 was first to report the relationship news. Reps didn't respond to a request for comment.