Diehard Rolling Stones fans must be wondering what the hell’s going on. The band reformed, charged hundreds of pounds for live tour tickets, and now that they’re finally getting to see their idols, people like Taylor Swift and Katy Perry are appearing on stage!

Fans of the We Are Never Getting Back Together singer won’t have been too bothered, though. Fans of really long song titles won’t have been, either. Swift joined Jagger on stage at their concert in Chicago on Monday, June 3. "Filing this under 'never in my wildest dreams.' Thank you Rolling Stones for inviting me to Chicago to sing with you," she Tweeted after the show, posting a picture of her and the legendary rocker to accompany it. It wouldn’t have been much of a surprise, though, as Jagger tweeted ahead of the performance, saying: "Looking forward to singing with @taylorswift13 tonight! Wonder which song we will do?"

She’s not the only mainstream popster to share the stage with the 70s giants; Katy Perry, too, got the chance to fulfil her dreams – dreams she probably only thought up when someone fooled into thinking she worked in music. She also thought Twitter would be the best place to boast about this. "Yes, I just did gyrated on Mick Jagger. What?!" she posted after the May 11 show. Lady Gaga, the Foo Fighters' Dave Grohl, Florence Welch and Tom Waits have all made guest appearances, too.

Taylor SwiftTaylor looks angry at having to carry all those awards

Katy PerryWe're guessing that most Rolling Stones fans couldn't point Katy Perry out in this line upRolling StonesThese guys will let anyone on stage