Florence Welch is to perform with The Rolling Stones at the O2 tomorrow (29.11.12).
The Florence and the Machine singer will duet with Sir Mick Jagger on the band's iconic track Gimme Shelter when the band perform the second of their 50 and Counting shows.
Welch will fly in from Luxembourg for the show and jet straight out to Germany afterwards, to continue her group's European tour.
A source told the Daily Mirror: "It is very, very tight indeed but it will definitely happen. You would never in a million years turn down the opportunity to duet with Mick on such an iconic song."
Welch, 26, follows in the footsteps of R&B star Mary J. Blige who performed the song with the band on Sunday (25.11.12), while legendary singer-songwriter Eric Clapton is also lined up to appear at one of the anniversary shows.
The source added: "Mary J. Blige did the female vocal part for the first show which blew the crowd away.
But Welch is determined to raise the bar even higher. It will be incredible.
"Eric [Clapton] is also taking part at some point, which will be historic too."
Tickets for tomorrow's sold out show are being re-sold online for up to £5,000, though some are available from LondonNet at around the £250 mark.
"It's a shame fans have been prevented from buying tickets at the original price," said a Stones spokesperson.
After tomorrow's show, the band will head to the US for shows at the Barclay Center, New York City.