The X Factor USA's four guests for the Judges' Houses have been revealed.

Justin Bieber, will.i.am, Nick Jonas and Marc Anthony will join regular judges Simon Cowell, Britney Spears, Demi Lovato and LA Reid to help select the final line-up for this year's live shows.

The 24 acts who have made it through to the Judges' Houses stage of the show will be revealed until the next episode of The X Factor on Wednesday, October 10 in the US.

The categories that each judge will mentor will also not be confirmed until Wednesday's show.

Last year's guest judges were Rihanna, Pharrell Williams and Enrique Iglesias.