Gary Barlow revealed that Leona Lewis was booed by The X Factor audience as she was a guest judge at the London auditions.
The former winner joined the panel at the O2 Arena when the auditions hit the capital.
Barlow confessed that he was not looking forward to the Bleeding Love singer being a judge, as he expected her to be boring.
He admitted: "I think people think Leona's a bit bland but she was great fun, even though she got booed."
Gary told Metro: "I had to tell her beforehand, `Don't let the audience sway you `cos they're a brutal crowd at the auditions'.".
Meanwhile, Barlow also gave his opinions on some of the other guest judges.
The singer said Geri Halliwell was "crazy" at the Liverpool auditions, while he was impressed with Rita Ora who helped out at the London auditions.
He said: "We also had Geri in Liverpool, who was crazy and lived up to expectations and we've had Rita Ora for the last couple of days who has been really great."
Meanwhile, Rita seems to have enjoyed her time on the panel and said she would like to join the show full-time.
She told Capital FM: "I said, whenever they need me, give me a call! I mean, obviously, I'm doing my own shows and I've got my album coming out, I'm still finishing my album.
"So obviously my music is the most important [thing], but there's a mixture,"
Rita added: "Whenever I can of course I'll be right back here!"
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