Taylor Swift joined the Rolling Stones onstage at Chicago's United Center last night (June 3) to perform 'As Tears Go By' -- and of course, dance a bit with Mick Jagger.

The Stones legend introduced the song as "one we haven't done in quite a long time. Actually, it's almost the first song that Keith (Richards) and I wrote. We didn't do it at the time, we gave it to someone else, a young lady, to sing. But we're going to do it now, with a bit of help..."

That assistance turned out to be country-pop sensation Swift, perhaps the most popular star in all of music over the last few years. The 23 year old sauntered in wearing a short black dress and handled the second verse herself. She also joined Jagger for a slightly exaggerated version of a formal dance, as if the two were crashing a ball at some palace. As she shared with her 28 million Twitter followers after the show, the night was clearly special for Swift: