Credit: Steve Jennings/

Guess Sean Penn and Robin Wright Penn haven't stayed in touch since she filed for divorced last year.

"She is a ghost to me now," Sean, 49, tells Vanity Fair in a new interview "We spent all those years together.... Now she's just gone."

Robin, 44, submitted divorce papers last August. The couple had been together since 1989 and wed in 1996. They have two children: son Hopper Jack, 16, and daughter Dylan, 19.

The spouses filed papers twice before -- in December 2007 and in April 2009 -- but reconciled shortly thereafter. Last year, the actress told More magazine lthat their marriage was definitely done. "I hit that crossroad a while ago...I know what I don't want."

Talking to historian Douglas Brinkley in Vanity Fair, Sean Penn explains that his split has helped him become more of an activist and humanitarian -- helping out in Haiti and other fragile, embattled parts of the world.

"I was for 20 years in a relationship with Robin and 18 years with children. I didn't have time to commit to anything--for real--in places like Iraq, except to denounce the war. But now I’m single. I can lend a hand."