By Breaking Celebrity News Staff

Best known for his serious roles and political activism, Sean Penn has been making headlines for his love life more than his movies lately.

The Oscar winning actor went public in July with a new, young mystery girl in July on a Malibu beach, a sexy brunette who some media outlets initially misidentified as Stacey Koplin.

Now Star magazine has exclusively revealed the woman in question is actually 26-year-old Shannon Costello, an aspiring actress and producer from Seattle who first met Penn,51, at a Los Angeles event party in the fall of 2009.

One Night With Quentin: Tarantino Is A Toe Sucker!

At the time, the Mystic River actor's wife, Robin Wright, had filed papers to end their 13-year marriage, but the divorce wasn't finalized until July 2010.

"There was an attraction between Sean and Shannon when they first met, but it was too soon after the break-up of his marriage, and her parents didn't approve at the time," an insider told Star.

Ironically, Shannon's new boyfriend is already friends with her uncle, outdoors writer Jo