X Factor chart Heroes: Finalists perform on charity single which will be in shops this month

Viewers will only find out who has made the last 12 on tonight's X Factor show, but already the finalists have recorded their first single.

The track, a cover of diva Mariah Carey's Hero, will be in shops on October 27, months before the winner is picked.

It will raise much needed funds for the Help for Heroes charity, which supports wounded troops, and the Royal British Legion's Poppy Appeal.

Anastasia Baker, left, and Laura Heatley could perform on the charity single Hero in aid of wounded troops- but only if they make the final cut on tonight's X Factor

Will they feature? Only the 12 finalists will perform on the charity single and tonight X Factor viewers will see them selected by the judges

An insider source told the Sun: 'I've never heard Simon more excited about anything - there's a real buzz about this single. It's going to blow everyone away when they hear it.'

The track will be performed live on the show for the first time on October 25.

Producer Cowell, 48, is said to be confident the track will head straight to the top of the charts.

X Factor supremo Simon Cowell is confident the song will top the charts

Will hopefuls Austin Drage and Diana Vikers compete for a place in the final - and on the Mariah Carey song

A source told the Star: 'It's a genius idea. in the past no-one has been allowed to release a song before the winner. But Simon has relaxed the rules and is releasing a single featuring all of the finalists.

'Not everyone who makes the live shows ends up with a record deal so this is a real gift for them.'