Aidan and Joseph O'Brien failed in their bid to complete a Derby double as Imperial Monarch finished a luckless eighth behind shock Prix du Jockey Club winner Saonois.
The father-son combination headed to France yesterday after a fantastic day at Epsom, with 2,000 Guineas hero Camelot completing a Classic double in the Epsom Derby.
The unbeaten Imperial Monarch appeared a leading candidate for the French equivalent following his victory in the Sandown Classic Trial last month, but found himself last turning for home after being shuffled back in a rough race.
Switched wide to challenge in the straight by O'Brien junior, the three-year-old found top gear and was flying at the finish, but was unable to reel in the leading group.
The honours went to Saonois, trained by JP Gauvin and ridden by Antoine Hamelin. Godolphin's Saint Baudolino took second in a bunch finish for the places. The British raiders failed to make their presence felt, with Brian Meehan's Most Improved (14th) and Ektihaam from the Roger Varian stable (15th) meeting traffic problems.
John Gosden's Gregorian trailed home 18th after running wide round the home turn, but the trainer enjoyed better fortune with Aiken, which secured his sixth successive win in the Grand Prix De Chantilly.
The trainer said: "He will be put into the Grand Prix de Saint-Cloud and the Hardwicke Stakes at Royal Ascot. The person who organises the rain will get us. I wouldn't want it too firm."
William Buick landed a double on the day as he guided Mick Channon's Laugh Out Loud to victory in the Group Two Prix De Sandringham and the filly will now head for the Coronation Stakes at Royal Ascot.