Demi Lovato will duet with Fifth Harmony in 'The X Factor' final - because she "didn't have anything else to do".
Show chief Simon Cowell - who is the group's mentor -joked it was "irritating" to have his fellow judge work with his act, but felt it best she had something to occupy her time because she has no contestants left in the competition.
Simon said: "It's kind of irritating to say but the person we decided to duet with is Demi Lovato.
"But then again she didn't have much else to do on the show because she hasn't got anyone else in the finals, I felt that she needed something to do."
And the music mogul "can't wait" to give his verdict on the performance after tiring of the 'Skyscraper' singer's constant criticisms throughout the series.
He added: "And after listening to your constant carping on about my contestants, the fact that I can now judge you, I can't wait."
Meanwhile, Britney Spears's act Carly Rose Sonenclar will take to the stage with LeAnn Rimes and the 13-year-old hopeful can't wait.
She said: "LeAnn Rimes is singing with me and I'm very excited about that.
"I think she is amazing and her voice is really, really special. I'm psyched."
Country singer Tate Stevens will perform with Little Big Town.
His mentor L.A. Reid said: "It'll be a bonfire."
'The X Factor' final takes place tomorrow (19.12.12) and Thursday (20.12.12).