Wild horses couldn't have dragged Taylor Swift away from the stage at Chicago's United Center on Monday night (June 3). The country pop sensation joined the Rolling Stones for a performance of their timeless ballad 'As Tears Go By' -- and she also got to dance with Mick Jagger.

The Stones leaked Swift's appearance at the final night of a three-night stand in Chicago via Twitter earlier in the day, but did not say what she'd be singing.

Jagger introduced the song -- which was a hit for Marianne Faithfull in 1964 before the Stones released their own hit version in '65 -- 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."

Jagger started off alone, with Swift casually strolling out to join in for the second verse before harmonizing with him on the refrain. The pair engaged in a playfully formal dance during the instrumental break, with Swift making elaborate gestures toward Mick -- who's a real-life knight.

Afterward, the delighted young star posted the above picture to Twitter, writing, "Filing this under 'never in my wildest dreams'. Thank you @RollingStones for inviting me to Chicago to sing with you."

The Stones have just a few more shows on their current 50 & Counting Tour, scattered over June and July. Swift is just one of the many stars from different genres who've made "surprise" appearances, including Keith Urban in Los Angeles and Carrie Underwood in Toronto.

Watch Taylor Swift Perform 'As Tears Go By' With the Rolling Stones