Joaquin Phoenix, who earned an Oscar nomination for his portrayal of Johnny Cash in "Walk the Line," says he is giving up acting so he can focus on his music.

The 34-year-old film star, who is the younger brother of late actor River Phoenix, has starred in "Parenthood," "To Die For," "Gladiator," "Signs," "The Village," "Ladder 49," "Walk the Line" and "Reservation Road."

Phoenix told E! News at Monday's benefit for the Association of Hole in the Wall Camps -- the late Paul Newman's charity -- that his latest film "Two Lovers" with Gwyneth Paltrow would be his last.

"I want to take this opportunity to give you an exclusive," Phoenix told E! News. "I've been through that. I've done it. No, I'm not kidding."

Casey Affleck, Phoenix's brother-in-law and "To Die For" co-star, who was also at Monday's fundraiser, told E! News Phoenix seems serious about the decision.