On Friday Chancellor Philip Hammond announced any Value-Added Tax collected on the winner's song will go to charity for the seventh year in succession.
Who won The X Factor UK 2017?
They then performed Demelo, one of their hit singles from this year's season.
Kevin, Grace Davies, and Rak-Su all performed Saturday evening in the first part of the final weekend.
This includes this year's victor Rak-Su, who are the first ever X Factor act to have had three No.1 singles on iTunes whilst being on the show.
The I'm Feeling You singers looked stunned as host Dermot O'Leary announced they had won the show, before hugging each other and their mentor Simon Cowell.
"I also have to say something else".More news: Ending the weekend with warm and cloudy conditions
More news: Ohio State makes its case to the playoff committee
More news: Explosive Device Defused at Christmas Market in Germany
"I want to say thank you to Just Eat, the panel, the contestants and the audience at home".
Rak-Su thanked viewers and their families for making it such a special experience.
Mentored by Simon Cowell, the foursome - made up of schoolmates Ashley, Jamaal, Myles, and Mustafa - have been firm favourites for much of the competition, with their original material being well received by the show's fans when made available on download and streaming services.
For the first time, all the money raised from the winning track will go to children's hospice charities Together For Short Lives and Shooting Star Chase.
Former Fugees star Jean said the boy band were "so incredible I had to jump on a plane to come represent for them, baby".
"And I don't wanna just rely on you guys. All the proceeds from the record [the winner's single] will go the charity".