Keating, himself a judge on the Australian X Factor, insisted that the Take That hitmaker is "just being honest" with contestants.
"He's not nasty. He's not at all! He's just being honest," he told Magic FM. "I think he's doing a brilliant job, I love him."
The Boyzone star added: "He's a good friend of mine and I get [his] good sense of humour and it's very much coming across. He's a real professional and his ability is outstanding, so I'm a fan."
Meanwhile, of his upcoming return to Australian X Factor, Keating teased: "Amazing talent, honestly I'm not just saying that. I mean, it's ten times the show it was last year.
"It's already with auditions going out on TV, it's already the number one show on the ratings, so very exciting."
The X Factor continues tomorrow at 8.15pm on ITV1.
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