Lenny Kravitz and choir
Lenny Kravitz was "just sitting up on the terrace having a drink and [he heard] some strange music." So he went and jammed with a choir. I want to believe this isn't some dumb staged viral marketing, but it was filmed by this guy and what are the odds that something like this would just happen spontaneously?

The one thing that leads me to believe that this happened organically is this YouTube comment:
Believe it or not, I am the electric guitar holding down the Jam and next to Mike Smeaton while he solos into another dimension. Lenny is a super humble guy and he shook my and the bands' hands. It was a once in a lifetime experience for a guy like that to show up and turn a 60 people concert to a 150-200 concert. Lenny, if you are reading this...Thank you so much for your exciting appearance, performance, and all around good will.