The five acts booted off The X Factor are returning to the show to join the seven remaining hopefuls for a performance of their charity single.
All 12 finalists sing on the cover version of Michael Jackson's You Are Not Alone, which will raise money for London's Great Ormond Street children's hospital.
Patients from the hospital will be among the studio audience on Sunday night to see Lucie Jones, Rachel Adedeji, Rikki Loney, Miss Frank and Kandy Rain return to the stage.
It is hoped the single, which goes on sale on Monday but is already available to pre-order, will repeat the success of last year's version of Mariah Carey's Hero, which raised more than £1 million for the Help For Heroes charity.
The show's current favourite Olly Murs said: "I'm a massive Michael Jackson fan so it's an absolute honour to be singing this, and the words relate so well to the kids at Great Ormond Street.
"Raising money for children worse off than us makes me really proud that we can make some kind of positive impact on their lives."
The contestants visited the central London hospital last month to meet some of the children who are receiving treatment there.
Twins John and Edward said: "It meant such a lot to us to meet the children at Great Ormond Street. It was really great to get to chat to them." They said they hope the single "will light up the faces of so many".
Fellow finalist Jamie Archer added: "It's really great that we've been able to use all the attention The X Factor has been getting and put it to good use."
Sunday's show will also see the remaining seven finalists cut down to a final six. Stacey Solomon is the last female contestant with a chance of this year's crown. The others hoping to win are Murs, Daniels, Archer, John and Edward, Joseph McElderry and Danyl Johnson.