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.
Photo gallery - Anastacia at Glasgow X Factor auditions:
Copyright: Rex Features Ken Mckay/Thames
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.