Collaboration.

Julian Lennon and Aerosmith's Steven Tyler have completed a song titled "Someday," which will be a bonus track on Lennon's Everything Changes album.

Julian Lennon and Aerosmith singer Steven Tyler have completed a song titled "Someday," which will be added as a bonus track to the U.S. edition of Lennon's Everything Changes album. The two wrote and recorded the song in mid-June and the final mixes were done yesterday, according to Lennon's Facebook posts.

Everything Changes was released in the U.K. last October and does not yet have an American release date. Lennon's sixth album is his first since 1998's Photograph Smile.

Julian is a guest on Aerosmith's upcoming album, Music From Another Dimension