Well, by "joined" I mean 11-year old Aidan Fisher basically tells Steel Panther guitarist Satchel to back the hell up because he's got this. Then Fischer proceeds to flawlessly launch into "Eruption/You Really Got Me" and the crowd goes nuts. Seriously awesome footage! Plus he's an 11-year old at a Steel Panther gig, which means his parents are awesome.
The whole thing took place December 19 at the Midland Theater in Kansas City, MO, where a small statue of Fischer was then erected outside.