The eight-year-old, a 33-1 chance, provided the raiders from across the Channel with their 10th victory in 11 runnings of the Group One contest.
My Best Valentine ran on strongly under Ray Cochrane to take care of another British- trained horse, Willie Muir's Averti, by two lengths with Sainte Marine third.
My Best Valentine was stepping up on all his previous achievements, having managed no more than a victory in a Listed race before and having failed to score all season.
His trainer, Vic Soane, a former jump jockey with Fred Winter, said: "We've been praying for rain all year and it has worked out just fine. This has to be the best day of my life.
"We do nothing with him at all. He's in a field all day and that is the way to train him. When he gets the saddle on him he really moves."
Britain, or rather the Dubai-Italian connection, secured another consolation prize when Godolphin's Fly To The Stars and Frankie Dettori, made all in the Prix du Rond Point.
"He's a tough horse and there might be another race for him before the season is out," Godolphin's racing manager, Simon Crisford, said. "He won't be going to America for the Breeders' Cup and we'll be taking him to Dubai for the winter."
n Jack Doyle, the legendary bloodstock agent responsible for the purchases of such famous horses as Mill House, Bruni and Right Tack, has died in a nursing home near Naas, Co Kildare, at the age of 83. He was honoured with a minute's silence during Saturday's meeting at the Curragh. His funeral mass will take place today at 10am at the Church of the Holy Redeemer at Bray, Co Wicklow, followed by burial at the Deans Grange cemetery.
n Ascot are considering a departure from tradition by allowing a form of private sponsorship to take place at the Royal meeting.
NB: Bay Of Delight
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