Marc Anthony has signed up to be a mentor on the US 'X Factor'.

The Grammy award-winning singer-songwriter will be working alongside Simon Cowell on the talent show, helping the music mogul pick his finalists for his category, which is believed to be the groups.

This news comes just over a week after it was revealed that pop star Justin Bieber had also been enlisted as a mentor on the show.

He was spotted at Simon's rival judge L.A. Reid's house helping him select the most talented acts from his category, rumoured to be the over-25s.

Justin - who was signed to Island Def Jam by L.A. - wrote on Twitter: ''Long day but great day. @LA_Reid @ScooterBraun just like old times! thanks (sic)''

New judge Demi Lovato is said to have enlisted the help of Nick Jonas to help her pick the best contestants and fellow new judge Britney Spears will be in charge of the 17 to 24 category. It is not clear yet who will join her during the Judges' House part of the competition.

'The X Factor' is set to begin on September 12 on Fox.