Music festivals are known for certain one-in-a-lifetime experiences. Last month at SXSW Usher joined The Afghan Whigs on stage at Fader Fort and provided a delicious dose of cognitive dissonance for the audience. It seems R. Kelly liked the idea so much that he hopped on stage during Phoenix's headlining set on Saturday. Naturally, a fan captured the moment on video. Embedded below is the video of the unlikely pair performing Kelly's "Ignition (Remix)" and a bit of "I'm A Flirt."