Brook was unveiled last week as the fourth judge on the popular show, which trawls Britain holding auditions to find new talent, joining Simon Cowell, Piers Morgan and Amanda Holden.
But the producers said that after reviewing tapes of the first auditions over the weekend, they had concluded the new line-up had not worked.
"The format of the show is cleaner and less complicated with just three judges, which was not fully appreciated ahead of filming," a spokeswoman for Talkbackthames said.
"Although Kelly brings a huge amount of warmth to the show and we've loved having her on board, the complications it adds to the filming process and format of the show means that unfortunately, and with huge regret, we have agreed with ITV not to proceed with a fourth judge."
A regular feature in the gossip pages, especially since she started going out with England rugby star Danny Cipriani, Brook has had to suffer tabloid taunts about her presentational skills before.
The 29-year-old Brook, who said last week she was a "huge fan" of the show, began her TV career as a presenter on "The Big Breakfast" but left after less than six months amid criticism of her performances.
"Simon has promised me some wild acts which I can't wait to see," she said after it was announced she was joining "Britain's Got Talent."
However, Cowell agreed bringing Brook on board had been a mistake.
"I have genuinely enjoyed working with Kelly: she is absolutely lovely and a complete professional," he said in a statement.
"But it's become clear the format doesn't support another judge and we will never add a fourth judge to the panel."
(Reporting by Michael Holden; Editing by Steve Addison)
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