Simon Cowell has sparked a war with Britain’s Got Talent co-judge Alesha Dixon by undermining her credibility.

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The argument erupted when dance group Lil’ Diamondz – who won Alesha’s Street Dance Stars on CBBC last September – appeared at the Birmingham auditions of the ITV1 show, and the 33-year-old star proudly gushed that they hadn’t let her down.

However, the 52-year-old music mogul was quick to hit back at her comment, branding her words of wisdom ”silly” and controversially saying, ”Who are you anyway?”.

He said: ”What a silly comment to make. That’s a silly thing to say, Alesha. Sorry, who are you anyway?”

After the 4,000- strong crowd gasped and booed at Simon, Alesha – who joined BGT from rival BBC One show Strictly Come Dancing in a reported £350,000 deal – was said to be ”really embarrassed” at the suggestion she was a ”nobody”.

A source told the Daily Mirror: ”Alesha obviously felt slighted. Everybody could tell because she clammed up and looked really embarrassed. Simon was reclining in his usual manner and didn’t seem bothered that he had just caused so much upset.

”Alesha was determined not to cause a scene in front of the audience but she really let rip behind closed doors. It was humiliating for Alesha that Simon suggested she is a nobody.

”This is especially the case when only a few months ago she was happily on another judging panel and Simon made it clear he wanted to poach her. She told her friends that she felt this dig had been out of order and stormed off to her dressing room.”

Despite the spat, a show insider claims Alesha had ”seen the funny side” by the next day of auditions.

The source added: ”He never intended to slight Alesha – it was all harmless banter. He always bickers with his fellow judges. It’s light-hearted fun which is just part of the show. By the next day’s auditions Alesha saw the funny side.”