The current Britain's Got Talent judge will be stepping in for Nicole Scherzinger at this weekends auditions in Manchester.
A source told The Sun newspaper: “Everyone is gutted that Nicole won’t be joining them, but Alesha has a wealth of experience from her role on BGT and her own pop career so will do a great job filling in.”
A spokesperson for The X Factor confirmed: “Alesha is guest-judging for the first day of the Manchester auditions as Nicole is unable to film that day due to a previous diary commitment.”
It's not the first time Nicole has been replaced, with last year's London try outs seeing Mel B stand in for the Pussycat Doll.
But she will be back for the rest of the auditions and later stages alongside Simon Cowell, Sharon Osbourne and Louis Walsh.
This year is the first time since between 2008 and 2010 that the panel has remained the same between series.
A source told The Sun newspaper previously: The chemistry was perfect last year, so it’s only natural to want to bring the same line-up together again.
“It’s usually hard to get people’s schedules to align but for the first year it has worked out."
The insider added: "The judges can’t wait to get started and have already been gossiping behind the scenes.”
Dermot O'Leary will be back to host the show while ITV2 spin-off Xtra Factor has been axed in favour of more online content instead.
Auditions in the judges' rooms began in Liverpool this week an will move on to Scotland after their stop in Manchester at the weekend.
The X Factor 2017 will start on ITV later this year.