Alien Uncovered - comprised of Madison, Natalie, Frank, Yaz, Shae and Temple - were the second act to be eliminated from the competition this series in the first week of the live shows.
But Sunday night's grand finale (13 December) saw the girl group return to the stage for a group performance, however, eagle-eyed viewers noticed that they were missing a member.
It's barely been a week since the girl group, who were mentored by Cheryl Fernandez-Versini, announced that Frank had gone her separate ways.
The girls revealed via Twitter: "Sometimes people part ways and although this is the end of a chapter we are really excited to show you guys the new Alien Uncovered! We want to thank you for all your endless support and we hope you continue to support us on this journey."
However, Frank had a different version of events, as she slammed the girls for "forcing her out" and said: "Big knock down after 3 years but I'm coming back stronger."
Frank tweeted: "Just to inform everybody that I was unexpectedly forced out of the band, by the other band members, who I thought were my friends. Obviously I'm devastated but with your support I'll bounce back."
Alien Uncovered, who are all former dancers, have been together for over a year.
It seems despite her exit, some fans were still hoping Frank would join the girls on stage during Sunday's X Factor final.
One tweeted: "Seeing Alien perform tonight won't be the same without @FrankArensMusic but you'll slay as a soloist girl don't worry."
Another fan said: "Wish @FrankArensMusic was performing tonight, but I'm sure she will be just as good solo."
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