The four-year-old fillies had the race between them in the final furlong, and at one stage it looked as though Tom Queally would lift the Group One prize on the Henry Cecil-trained Timepiece.
Queally had his mount ideally placed in second as Lily Of The Valley made the running, moving smoothly to the front when he asked her to quicken.
However, Maxime Guyon had other ideas on Announce and drove Andre Fabre‘s charge into the lead in the last 100 yards to grab the spoils by a short neck, with two and a half lengths back to Lily Of The Valley in third.
“That was great. They‘ve run super races, both of them,” said the owner’s racing manager Teddy Grimthorpe, who on Wednesday saw Twice Over and Midday dominate the Abdullah-sponsored Juddmonte International at York.
“That was a first Group One win for Announce and Timepiece has already won one (the Falmouth Stakes), so it‘s good for the stud.
“We‘ll see how we go before making plans. Obviously we‘ll try to avoid each other now.”
Frederick Engels was strongly fancied to be the third successive British trained winner of the Darley Prix Morny after Dream Ahead and Arcano, but David Brown‘s colt failed to fire in a race won impressively by Dabirsim.
Given a confident ride by Frankie Dettori, his only mount on the card, the unbeaten Dabirsim took the field apart with a terrific turn of foot a furlong out to secure win number four.
Family One made a sterling job of trying to make all the running, but had no answer to the Christophe Ferland-trained colt, who swept by in the style of a potentially very smart performer to win by three lengths.
Vladimir was third and Sofast fourth, with Frederick Engels only fifth having had every chance in the hands of Johnny Murtagh.
Murtagh had the Windsor Castle and July Stakes winner sat in second early on, but he could not pick up when it mattered.
It was reported afterwards that Frederick Engels coughed at the start.