Robbie Williams is set to join Sharon Osbourne on 'The X Factor'.

Robbie Williams

Robbie Williams

The 42-year-old singer will help Sharon, 63, decide on her acts for the live shows when he joins her at her Los Angeles mansion for Judges' Houses.

A source told The Sun: "Getting Robbie back on the show is a really clever move on the part of Sharon and the producers.

"He has a huge fanbase and will attract loads of extra viewers purely from his name.

"It's that sort of star quality they need to compete with 'Strictly'.

"Robbie and Sharon are old mates and used to be neighbours in Los Angeles so their chemistry is amazing.

"Every time Robbie appears on the 'X Factor' he proves great entertainment value.

"As they never managed to get him to be a full-time judge, this is the next best result."

Robbie previously appeared on the show with Sharon in 2013, when he helped her pick Sam Bailey, who went on to win.

Presenter Dermot O'Leary - who was replaced by Caroline Flack and Olly Murs last year - recently revealed he is thrilled to back and to have Sharon, Louis Walsh and Nicole Scherzinger returning to the show.

He said: "Sharon being back adds a little oomph to Louis and he stands up to Simon a little bit more. Nicole is brilliant because she is so beautiful and intelligent and really funny."