Watch: Taylor Swift joins The Rolling Stones on ‘As Tears Go By’ in Chicago

Taylor Swift did her best Marianne Faithfull imitation Monday night in Chicago as she became the latest artist to join the Rolling Stones on stage.

[More after the jump…]

Dressed in flats (and still taller than Mick Jagger) and a black top and shorts onesie Swift casually wrapped her arm around Jagger”s shoulder and then owned the stage as she went toe-to-toe (literally at some points) with Jagger on “As Tears Go By.”  Jagger and Richards wrote the tune, but gave it away to Faithfull, who had a hit with it in 1964.  They recorded it the next year.

Swift seemed to have no stage fright or nerves at all given that she was singing with rock and roll loyalty (though we feel for her around the 3-minute mark, when she looks to see where Jagger is and he”s switched to the other side).  In fact, we don”t know if we”ve ever seen her this collected. We sure wouldn”t have been.

However, her natural ebullience returned shortly thereafter when she tweeted “filing this under ‘friends forever,”” and posted a backstage shot of her and Jagger with their arms around each other. She next tweeted, “Filing this under ‘never in my wildest dreams.” Thank you @RollingStones for inviting me to Chicago to sing with you,” along with a photo of Jagger bowing to her and holding her hand.

Among the other artists who have joined the Stones on stage during their 50th anniversary jaunt are Gwen Stefani, John Fogerty, Keith Urban, Carrie Underwood, and Dave Grohl.

×