During an interview with Xtra Factor host Caroline Flack, Willoughby revealed that Arthur's Motown performance of Marvin Gaye's 'Let's Get It On' had wooed her.
© Photofab/Rex Features
© Rex Features
"It was so good. When he performed 'Let's Get It On' - I was watching it going, 'I now really fancy you' - it was amazing!" said Willoughby.
Flack added: "In my opinion, his performance was one of the best X Factor performances I've ever seen.
"When I found out that he was doing that song, I knew that he was going to nail it and I was really excited all week for Saturday to see him do it."
Watch James Arthur's performance of 'Let's Get It On' below:
James Arthur, Christopher Maloney, Union J and Jahmene Douglas are the four remaining acts hoping to triumph on this year's X Factor final.
The X Factor semi-final airs on Saturday, December 1 at 9pm on ITV1.
Photo gallery - X Factor results show 8:
Copyright: Ken McKay/Thames/Rex Features
