The fan (Sydney Bourbeau) was on stage at a mall in Edmonton singing an Ed Sheeran song as part of a fundraiser. Ed just happened to be in same mall, heard Sydney singing his song, and surprised Sydney (and everyone else) by jumping up on stage to sing with her. This is one of many reasons why we love Ed Sheeran.
WATCH as Ed Sheeran gives a surprise serenade to a couple on their wedding day
Ed should have dropped the mic at the end of the video, because he won the internet today.