Ridden by Thierry Thulliez, Carling took up the running a furlong and a half from home and beat Matiara by a neck, with the German-trained Tryphosa three-quarters of a length back in third.
Caramba, the British challenger ridden by Pat Eddery for Richard Hannon, finished seventh, beaten little more than two lengths behind the 7-2 winner after being held up in the early stages.
Corinne Barbe, the winning trainer, said: "I'm not used to working out the programme for a Diane horse and first we want to enjoy the moment. But she's in the King George and we might think about the Breeders' Cup."
Andre Fabre, the trainer of the disappointing Derby favourite Pennekamp, suffered another disappointment when the 6-5 favourite, Muncie, could finish no better than fifth.
Prix de Diane Hermes
1. Carling (T Thulliez) 3.5-1.
2. Matiara (F Head)
3. Tryphosa (A Boschert)
(Winner trained by Mrs P Barbe, France, for Ecurie Delbart)
12 ran. Unplaced favourite Muncie (coupled with Tamise) 11-10.Reuse content