Thanksgiving day 1974 John Lennon paid off a wager he lost with Elton John by joining him on stage at Madison Square Garden. While recording Lennon's "Walls And Bridges" album Elton helped out on the song "Whatever Gets You Through The Night".
Elton told John that in return if the song hit #1 on the charts that John would have join him on stage Thanksgiving night at the Garden. Well the song hit #1 and the rest is history. Unfortunately it turned out to be John Lennon's last public appearance. Watch it here.