The actor, who starred in Juno and Scott Pilgrim Versus The World, played with the band at The Moore theatre in Seattle on Tuesday (November 30), when they supported Passion Pit.
A Sub Pop representative confirmed his role in the band, telling Thestranger.com: "As of right now he is not an official member, just playing with the guys on this tour."
Mister Heavenly also include members of Modest Mouse, Man Man and Islands. They continue their tour of the US throughout December.
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