Washington, Dec 15 : Hollywood legends Marlon Brando and Robert Duvall once opted for a unique way to lighten the mood on the sets of the Godfather - flashing their butts at cast and crewmembers.

In a new picture book Godfather Family Album, James Caan, who played Brando''s onscreen son Santino ''Sonny'' Corleone revealed the prank that both the actors played on the sets of 1972 movie.

He said that Brando was the ultimate joker.

"They''re standing at the wedding ceremony when they posed for that picture, and there are 500 extras, old ladies, old men, kids, everybody," Contactmusic quoted Caan as saying.

"Bobby Duvall sees the ultimate moon. He and Brando had a race to drop their pants and Bobby''s got hitched, and Brando beat him, bent over and spread his cheeks and mooned everybody.

"We had this belt made; Moon Champion, hand-tooled leather. Brando got it," he added. (ANI)