The members of Aerosmith, including lead singer Steven Tyler (2nd from L), pose backstage after performing during the 11th season finale of American Idol in Los Angeles. Reuters Photo/Jason Redmond
Frontman Steven Tyler introduced the star to the stage, telling the crowd, "I need a little help up here. Johnny Depp, are you in the house?"
Depp then walked on and played guitar on classic track Train Kept A-Rollin' for a crowd which included Tyler's actress daughter Liv and funnyman Jim Carrey.
After the concert, Depp joined the band for an afterparty at a Mexican restaurant on the Sunset Strip with other famous faces including Alice Cooper and Breaking Bad star Aaron Paul.