Diamond Necklace kept her unbeaten record intact with a commanding two-and-three-quarter-length victory in the Qatar Nassau Stakes at Glorious Goodwood on July 30, 2026 — her fourth career win at Group One level, the highest tier of Flat racing.

Sent off at 5-2 under Ryan Moore, the Aidan O'Brien-trained filly saw off four rivals on day three of the five-day Goodwood Festival. Friendly Soul, the 9-2 second favourite trained by Thady Gosden, could only chase her home. The race, restricted to fillies and mares aged three and older, carried a guaranteed purse of £600,000 Racing Post.

The winning margin told only part of the story. This was Diamond Necklace's sixth straight win from six starts, and her most emphatic yet. In June she landed the Prix de Diane — the French Oaks — at Chantilly by a nose, grinding out a gutsy finish that extended her record to five from five. At Goodwood, against a field that had been reduced when the David O'Meara-trained Pretty Polly Stakes winner Estrange stayed at home, she won with something in hand Thoroughbred Daily News.

Gosden, who watched his charge fill the runner-up spot, was generous in defeat. He described Diamond Necklace as "exceptional" after the race, while noting that Friendly Soul was continuing her own return to form after what connections called a horror start to the season Racing Post.

What comes next is where the picture broadens. O'Brien confirmed afterwards that the Prix de l'Arc de Triomphe — Europe's most prestigious Flat race, run at Longchamp in October — is "possible" for the filly. "The next run will tell us where she is going to go after that," he said The Guardian.

The options O'Brien listed read like a compass of late-summer targets: an Arc trial, a fillies' race at Deauville in August, or a race at Leopardstown in September. Each would serve as a stepping stone toward — or away from — a Longchamp tilt in the autumn.

Bookmakers responded to the Nassau Stakes win by trimming Diamond Necklace to 10-1 for the Arc, placing her third in the betting behind Daryz, last year's Arc winner, and Constitution River — another O'Brien trainee, who has already landed the French Derby and Eclipse Stakes and is heading for the International Stakes at York. The stable's strength in depth is striking: earlier in the season, Minnie Hauk, runner-up in the 2025 Arc, was regarded as the leading Ballydoyle candidate for this year's race Racing Post.

Betway had already cut Diamond Necklace from 14-1 to 10-1 after her Prix de Diane win in June Racing Post. The price has held firm through Goodwood, a sign that the market wants to see one more run before committing further.

For now, the filly with the unbeaten record and the Group One résumé has done everything asked of her. The next start, wherever O'Brien sends her, will shape the autumn.