The BBC was left reeling by Alesha's decision to join the ITV1 show's judging panel.
It was dubbed an act of revenge by Cowell after Strictly's ratings victory over the mogul's other TV show, The X Factor.
Cowell ? who was snapped with fans on a beach in Barbados yesterday ? said he wanted to "change the perception" of BGT by making it "younger and better".
The 52-year-old will return to the judging panel full time alongside Amanda Holden, 40, and new signing David Walliams.
He said: "I love Alesha. She's feisty, opinionated and knows what it's like to be a competitor and judge. She is going to bring a lot to the table.
"And I'm delighted David is joining. He thinks he can do a better job than the people there before so it will be fun. I think he's terrified!"
The last time the show had four judges ended in disaster. Cowell axed Kelly Brook after just a few days in 2009 insisting "BGT just doesn't work with four people".
His full time return follows pressure from ITV who saw The X Factor and BGT slip in the ratings without him.
He has only judged the final week of the last two series after declaring he was "bored" of sitting through the auditions.
But he said yesterday: "I miss the British public, and I miss judging them. I've worked in America all this year but now I've got itchy feet again.
"I want to find the next generation of talent. Different and new acts, younger and better talent.
"I want to change the perception of the show. I think there's a notion that all we want is older people who sing opera."
Former Mis-Teeq singer Alesha, 33, who won Strictly in 2007 before becoming a judge, said yesterday: "I'm delighted to be joining the panel on BGT. It's a fantastic show and I'm very excited."
Little Britain star David, 40, added: "I am so thrilled to be the new Cheryl Cole."
The move threw a lifeline to former Strictly judge Arlene Phillips.
Arlene, 68 ? who was replaced by Alesha three years ago amid an ageism row ? said: "I will be gathering my thoughts and I will certainly have some things to say."
Cowell also announced he will put up ?250,000 of his own cash to double the prize to ?500,000. The winner will also perform at the Royal Variety Performance.