Royce thought the 'I'm Outta Love' singer was an American tourist and after chatting to her for 45 minutes over breakfast at a Glasgow hotel, offered her tickets to be in the audience.
The US star is the latest guest judge to help out at the auditions stage of the ITV1 reality show and is thought to be in the running for a full-time position on the show alongside Mel B, Geri Halliwell and Rita Ora.
She has previous reality TV experience from working as a judge on Channel 5's Glee-inspired reality series Don't Stop Believing.
Anastacia tweeted this morning: "I would like to send a super big shout out to the whole team The X Factor. I had the best time.
"Such a lucky lady to be sitting next to the charming and talented Gary Barlow. But guess what? I think I am crushing on the wild Louis Walsh."
X Factor auditions finish later this month following dates in Cardiff and Newcastle.
