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.