Late BEATLE John Lennon's son SEAN has enlisted the offspring of another rock superstar, Paul Simon, to work on his forthcoming album. HARPER SIMON has been helping Sean Lennon record FRIENDLY FIRE, his first album since 1999. An insider says, "Sean and Harper obviously have a lot in common and are good friends. "They know it's virtually impossible to escape from their fathers' shadows but they've had a lot of fun putting the album together." Friendly Fire is due to be released in September (06).