The broadcaster, 61, who has been on the judging panel since the show's debut series in 2020, is set to return for its fourth series, which is expected to air early next year.
He spoke about the series whilst at the ITV Palooza on Tuesday night as he joined a slew of celebrities in attendance at the event in London, which showcases ITV 's upcoming projects.
Discussing the Masked Singer, Jonathan teased a huge celebrity will on the new series and said the judges thought there was "no way" they would be involved in the show.
He commented: "I'm not sure what I'm allowed to say. I will tell you one thing; there's a genuine stadium filling name on the show. It's someone we were all amazed to see."
Jonathan add: "[We were] all surprised". He suggested that himself and his fellow judges thought there was "no way" the celebrity would be involved in the Masked Singer.
"I think their name had come up I think some of us dismissed it," he explained. He added: "We thought there's no way this person will be on the show but they were".
Whilst on the red carpet, Jonathan revealed that he likes reality TV shows. He however said his wife has told him he can't go on Celebrity Big Brother if it returns.
He said: "I like reality shows. Who knows [whether I'd do more]? Now ITV has bought back Big Brother, if they bring back a Celebrity Big Brother maybe I will do that".
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He added: "But my wife has always said I can't go on Big Brother or any of those shows. Partly because she wants me at home, partly because she doesn't want people to see me snoring."
Jonathan suggested that he wouldn't fancy I'm a Celebrity. When asked if he would be up for the show, he responded: "Well I'm vegan, I don't want to eat bugs and stuff."
When it was pointed out Boy George, who is vegan, is a campmate this year, Jonathan said: "Yeah but he's getting off lightly. Some of the stuff he ate in the challenge I'd eat at home."
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