Johnny Depp joined Alice Cooper onstage during a club gig in London on Sunday night.

Before the show, Alice posted a picture on Facebook of Johnny holding a guitar backstage . . . with the caption:  "Johnny Depp!!  Waiting to jump on stage with Alice for '18' and 'School's Out'!"

Here's that picture:

Johnny played "18" with the band, and then they did a cover of Pink Floyd's "Another Brick in the Wall", which led into "School's Out".

Luckily, there are videos on YouTube of both "18" and "School's Out". The quality isn't great, but it's not the worst, either: