Image source, Getty Images
Image caption,Ryan was British all-weather champion jockey last season
Bluestocking gave trainer Ralph Beckett and jockey Rossa Ryan their biggest win with victory in the Prix de l'Arc de Triomphe at Longchamp.
The four-year-old had been added to the field at a cost of £100,000 by owner-breeders Juddmonte after her impressive win in the Prix Vermeille at the Paris track last month.
The filly, who went off at 5-1, tracked the Aidan O'Brien-trained Los Angeles and Ryan Moore from the start.
She dug deep to finish strongly and hold off runner-up Aventure, with Los Angeles third, to land a record seventh win in Europe's richest race and £2.4m prize money for the late Khalid Abdullah's racing operation.
"She is an extraordinary beast," Beckett told ITV Racing.
"The draw helped. Rossa got her in the right place - everything went to plan and this is our best-ever day."
Ryan, who has ridden Bluestocking in her past seven races, said: "A horse can change your life - and she has mine."
Bluestocking had been backed down from 12-1 overnight and follows Rainbow Quest (1985), Dancing Brave (1986), Rail Link (2006), Workforce (2010) and Enable (2017 and 2018) as Juddmonte-owned winners.
"It's extraordinary really. I grew up watching Rainbow Quest and Dancing Brave, so to train a winner in these colours is a huge thrill," said Hampshire-based Beckett, who was second with Westover last year.
There was sad news after the race with confirmation that Haya Zark - who had been pulled up by jockey William Buck - was fatally injured.