They will also be the first X Factor victor to release their own original track Dimelo as their winners single.
They then performed their winners' single again, with Grace and the rest of The X Factor 2017 contestants joining the band on stage. They have released their winner's song Dimelo.
Fans raced to Twitter confessing they were unable to use the X Factor app to vote for one of two reasons.
The X Factor 2017 victor has been revealed in tonight's final results. On Saturday, One Direction's Louis Tomlinson performed new single Miss You, while LA boyband PrettyMuch performed their debut single No More live for the very first time.
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Simon said: "I want to say first of all congratulations to Grace who is really an outstanding artist". This doesn't get paid for for nothing.
Following his elimination, Kevin told Dermot: "Thank you the United Kingdom for believing in me to put me on that stage".
Meanwhile Kevin Davy White performed a cover of George Michael's Fast Love alongside Britain's Got Talent victor and multi-instrumentalist composer and producer Tokio Myers, while Rak-Su teamed up with Wyclef Jean and Naughty Boy for a version of their original track Dimelo.
Cowell also urged viewers to help them raised £1 million for the children's hospice charities.
Former Fugees star Jean said the boy band were "so incredible I had to jump on a plane to come represent for them, baby". You can go to the website, donate whatever you can. "All the proceeds from the record [the winner's single] will go the charity".