Bluestocking scooted clear of her rivals to win the Prix de l'Arc de Triomphe – and land a major gamble.
The British-trained filly, ridden by Rossa Ryan, was always in the perfect position and was sent to the lead two furlongs out.
She held the challenge of Aventure to land Europe's richest race at ParisLongchamp.
Bluestocking was backed into 5-1 from 12-1 in the hour before the race.
Winning trainer Ralph Beckett said: "It's a tribute to her constitution as much as anything. It's extraordinary to have a horse to start in May and dance all those dances, the King George, the Juddmonte (International), and get beaten and come back and do that.
"After only three weeks and what looked like a tough race in the Vermeille, it's extraordinary. She is an extraordinary beast.
"I think the draw helped, it was terrific. He got her into the right place and everything went to plan, he was able to pull it off.
"Westover hit the front with a furlong left last year and I was kind of waiting for something else to come and get her, what a day.
"This is our best ever day, it has to be. I've been lucky enough to win a couple of Oaks but this is our best day, for sure.
"Barry Mahon and the Juddmonte team are an extraordinary outfit to work for in that there is no pressure, ever.
"Good horses train themselves. Amazing, really. I never thought she'd win."
A jubilant Ryan added: "I know everyone overlooked her, but on form she had been at the top table and done it all. She just proved she's something else.
"I can't really believe it, this filly has been something else to my career.
"My family are here, they all came over and it's very surreal."
