The Rockstar Energy Drink Mayhem Festival featuring Slipknot, Slayer, Motorhead, Anthrax and others made a stop in Auburn, Washington on Tuesday and during Motorhead's set, fans got a surprise when Duff McKagan joined the band on stage for a performance of "Killed By Death".

Duff played bass in Guns N' Roses and Velvet Revolver, but played guitar with Motorhead for one obvious reason, LEMMY.

You never know what you're gonna see at a rock show.  Here's more proof of that...