Simon Cowell was left red faced after failing to recognise Lee Nelson during auditions for Britain's Got Talent, according to reports.
The comedian - real name Simon Brodkin - impressed the judges as a rapping rabi during the London auditions, the Daily Star reported.
A source told the publication: “Lee’s rapping rabbi was the talk of the day’s auditions and had the whole crowd on their feet.
“Even Simon, who is hardly ever swayed by a joke act, was into it and all four judges gave him a ‘Yes’.
“I have no idea how someone as well-known as Lee slipped through the net."
It is not the first time the comedian has hit the headlines with his pranks.
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Last year he burst into a Fifa press conference and threw money at president Sepp Blatter.
He also invaded Kanye West’s Glastonbury headline set before being escorted off by security.
Britain's Got Talent returns to ITV later this year.