Brown Panther was a big disappointment as Les Beaufs made all of the running to take Group One honours in the Prix Royal-Oak at Longchamp.
Tom Dascombe's stable star finished towards the rear along with fellow British challengers Quiz Mistress and Hurricane Higgins.
Julien Guillochon's tactics on Les Beaufs paid dividends with the three-year-old gelding opening up an eight-length advantage at one stage in the near two-mile feature.
Les Beaufs (9-1), trained by Valerie Seignoux, never looked like stopping and won by four and a half lengths from Silver Valny, with Rollex Borget third.
Verema was fourth and the 7-4 favourite Dalkala only fifth.
Dascombe later tweeted: "Spoken to Richard Kingscote who just said that the horse ran very flat.
"That'll obviously be it for the season and there will be other days."