Jessie J 'could not be harsh judge' on X Factor

Jessie J "couldn't" be an 'X Factor' judge.

The 'Do It Like a Dude' hitmaker - who recently assisted Tulisa Contostavlos at the Judges' House stage of the ITV1 competition - has signed up to be a mentor on BBC singing show 'The Voice', but would be unable to appear on its rival show, because she wouldn't be able to hand out harsh critiques to struggling contestants.