Saturday's show was scheduled to have the acts performing tracks from their idols and musical favourites in a Heroes Week, but due to a last minute production switch, plans have been changed.
Rock Week has proved popular in previous series and last year's edition included a memorable performance of 'Creep' from Wagner, Matt Cardle's 'Nights In White Satin' and Katie Waissel's 'Sex On Fire'.
A source told Digital Spy: "Producers wanted to spice things up a bit for viewers and they thought the return of Rock Week would provide plenty of drama. It will challenge some of the acts, who have had an easy ride so far."
An official X Factor rep said: "The change of theme weeks was a production team decision to take contestants out of their comfort zone. Production regularly change themes late in the day."
The X Factor Rock Week airs on Saturday at 8pm on ITV1.
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