Mo was voted the victor, with the hotel worker appearing stunned as she called out his name.
Well Gavin - who didn't have any acts going into the final - has admitted he's not (yet) been asked to return: "I think they're waiting until the end of the series".
Mo will now release his new single as a signed recording artist.
Jennifer's other contestant Jamie fell by the wayside during Sunday night's show, with his rendition of Ed Sheeran's Shape Of You not proving to be enough to carry him into the final round.
During tonight's show, the three remaining contestants sang once again for the chance to win the coveted prize.
She had broken down in tears over his final performance.
Jennifer gave her advice for aspiring singers and said: "Just believing in yourself, being your best you and trusting that and always trying no matter what".
She told The Daily Star: "I've already said I will come back". I don't see why I wouldn't.
Following the announcement, Mo said: "I just want everyone to know from the blind auditions onwayds they have done unbelievable".
And Gavin admits that is he doesn't get invited back in his spinning chair, he'll feel it's because he's done something "wrong". I've had a great time'.
Yet that wasn't even the strangest thing to happen during the finale, with Sir Tom's X-rated blunder followed by an intrusive fan hopping onstage with some type of sign he was attempting to show to the cameras.