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Could Diamond Necklace claim glory for Aidan O’Brien in 2026 Prix de l’Arc de Triomphe?

Diamond Necklace has been backed into 8/1 odds for the Prix de l’Arc de Triomphe, with Aidan O’Brien hoping his three-year-old filly can pass a new stamina test at Longchamp.

by
The Racing Ahead Team
1 October 2026

Diamond Necklace was in a league of her own in the Nassau

Bookies have slashed the odds of Diamond Necklace ahead of this weekend’s Prix de l’Arc de Triomphe, as Aidan O’Brien searches for only his third victory in the famous race.

O’Brien last won Europe’s richest Flat race a decade ago with Found in 2026, with his first victory coming in 2007 with Dylan Thomas.

This year the master of Ballydoyle has pinned his hopes on Coolmore’s three-year-old filly, who has won six of her last seven outings.

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Diamond Necklace faces stamina test

She won the Prix Marcel Boussac at Longchamp in 2025, but was handed her first defeat in Deauville in the Prix Jean et Louis Romanet just over a month ago.

O’Brien has kept his powder dry with Diamond Necklace, trusting to test her stamina over the longer trip on the big day this Sunday afternoon.

“We can’t be sure with Diamond [Necklace] whether she’ll get the mile and a half,” said O’Brien.

“That type of filly over the years has got it and I know a lot of them have run in the Vermeille.

“We had one eye on America as well and we didn’t want to stretch her.

“Sometimes when you run them over a mile and a half for the first time, they can have a very hard race, even though they might win and they might get it.”

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Other hopes

Benvenuto Cellini and Minnie Hauk are O’Brien’s other Prix de l’Arc de Triomphe hopes of landing him a trio of Longchamp wins.

Bookies remain bullish about Diamond Necklace’s chances, though the wetter weather could play a part and see her odds drift in the build-up to the race.

Brian O’Keeffe of Boyle Sports said: “We have a unique situation ahead of this year’s Arc, but plenty of punters are nailing their colours to the mast for Europe’s greatest race even before the draw is revealed.

“Daryz remains a well backed favourite on the back of Francis-Henri Graffard’s bullish comments, but Diamond Necklace is the real money horse, seeing her odds slashed into 8/1 from 20/1, as Aidan O’Brien hunts down a first win in the race in a decade.”