Mick Jagger and Taylor Swift duet at a Rolling Stones show in Chicago.

Taylor Swift teamed up with Mick Jagger for a surprise duet during The Rolling Stones’s stop-over at Chicago’s United Center last night (June 3). It was a touching performance of “As Tears Go By.” Taylor even sang off-key right along with Mick!

It was age combined with beauty, a fitting tribute to the Stones’ 50th anniversary tour, since Sir Mick, 69, is nearly a half century older than Swift, 23.

Still they made a fetching couple as the held hands and sang together. Who knows maybe they’ll even start dating. After all, Taylor is available and Mick, well, he has a girlfriend, but that hasn’t stopped him in the past.

The Stones, incidentally, released “As Tears Go By” in 1965, nearly a quarter century before Swift was born. So even the song is old enough to be her father. But, hey, like many Stones songs, the tune is timeless.

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Mick and Keith Richards actually wrote it in their first collaboration for UK folk singer Marianne Faithfull, whose four-year love affair with Mick ended disastrously in a 1969 drug bust.

In fact, Taylor actually looks a lot like Marianne on stage. Now 66, Faithfull is still performing in small venues in Australia.

Swift was thrilled with the chance to sing with the Stones.”Filing this under ‘never in my wildest dreams’.Thank you @RollingStones for inviting me to Chicago to sing with you,” she Tweeted after the show.

The Stones have added special guests at almost every stop on their tour, from soul singer Mary J. Blige and Bruce Springsteen, to Lady Gaga, Tom Waits, Katy Perry, Keith Urban and Carrie Underwood.

Watch Taylor and Mick sing below and follow TheImproper on Twitter to keep up with the latest music news.