The runner-up of the 2012 show said he wants Hannah Barrett, who is being mentored by Jahmene's former coach Nicole Scherzinger, to win this year's series.
He praised Barrett's "soulful" vocal while on the red carpet for the Pride Of Britain Awards on Monday.
And the winner of last year's 'X Factor' James Arthur has also backed Barrett.
He recently tweeted: "Hannah has to win this year for me. That is what you call soul! Take note on how to believe in what your singin from this girl!"
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Watch The Pride Of Britain Awards on ITV on Tuesday 8 October at 8pm