Adele - Adele Eyes X Factor Appearance

The Rolling in the Deep hitmaker was reportedly approached to appear as a guest mentor during the talent show's selection process, helping either Kelly Rowland or N-Dubz star Tulisa Contostavlos to choose their favourite acts.

But she was forced to refuse the offer due to her hectic work schedule, and will duet with a contestant during the show's final in December (11) instead, according to Britain's Daily Star Sunday.

A source tells the publication, "Simon is desperate to get Adele involved on this year's show. There's no denying Adele is the biggest singer in the world right now and Simon wants her to appear on both the U.K. and U.S. X Factors.

"He couldn't get her for the judges' houses stage, so he now wants her to sing with one of the contestants on the grand final in December."