Katy Perry's Prismatic World Tour was across the pond last week and after her second show at London's O2 Arena a very special guest dropped by back stage.

The illusive Adele made an appearance and even posed for a selfie with Perry.

I guess Adele is a fan of Katy's and came to see the show. Pair that with her recent cryptic tweet about hearing from her soon and I get my hopes up for a Katy Perry/Adele duet!

Honestly I can't even imagine what the song would sound like, but presumably it would be about a break up. I mean they both write a lot of relationship stuff.

Either way, I think it's pretty cool she came out to support a fellow pop star and they both look amazing in this picture. And if a track comes out of it, that would be cool too!