Former New York mayor Rudy Giuliani has been revealed as a contestant on the US version of The Masked Singer, causing judge Ken Jeong to walk off in disgust.

77-year-old Giuliani, who has been mired in controversy in the US over allegations he made misleading claims about the 2020 US presidential election, had been competing on the show wearing a Jack In The Box costume.

It was previously reported that Giuliani - a former lawyer for Donald Trump - was a contestant and newly released clips show the judges looking stunned as his mask came off.

Comedian Jeong walked off as Jack In The Box's identity was revealed, saying, "I’m done."

Host Nick Cannon joked that it was a surprise to see Giuliani on The Masked Singer.

"I guess the main reason is I just had a granddaughter, Grace, and I want her to know that you should try everything, even things that are completely unlike you and unlikely," Giuliani said.

"I couldn't think of anything more unlike me and unlikely than this." he added, before singing sang a rendition of the song Bad To The Bone.

However, some viewers were less than impressed by the appearance from the controversial ex-mayor and Trump ally.

"Giuliani???" one said on Twitter.

"Seriously? Rudy Giuliani," said another.

One fan said the reveal was a "shocker".

Another said: "I don’t know who thought it would be a good idea to put Rudy Giuliani on."

"Giuliani on The Masked Singer isn't even registering as reality in my brain," said another.