The model showed off her vocal abilities back in host Dermot O'Leary's dressing room, belting out Whitney Houston's 'Greatest Love Of All'.
Kate's impromptu singsong was revealed by 'X Factor' executive producer, Mark Sidaway, who tweeted after Sunday's show: "Well that was fun. Twerk free zone and Kate Moss in @radioleary dressing room singing The Greatest Love of all #xfactor @TheXFactor."
A source told The Mirror: “Kate was excited to meet the two girls – and they were ecstatic to meet her.
“It was a nice surprise for them and they were both a little bit starstruck when Kate appeared backstage, especially as she was asking to see them and not the other way around."
Kate has long been a fan of 'The X Factor', and was even linked to a fashion role on the show last year.