In contrast True Love and Precise are set to go to the paddocks after the Breeders’ Cup for a meeting with Justify, while four-year-old Minnie Hauk is set for a swansong in Japan before joining them.

But the other trio will race on next year and O’Brien is convinced that Constitution River will prove himself after admitting trainer error in not giving him his best chance by dropping him to a mile at Ascot on British Champions Day.

“Constitution River is staying in training next year. I messed up and picked the wrong race for him, but we are keen to race on next season,” said the Ballydoyle trainer.

The Wootton Bassett colt won the Dee Stakes, Prix du Jockey Club and the Coral Eclipse in the early part of the season, prompting O’Brien to single him out as a special talent.

But three defeats in the second part of the campaign, at York in the International behind Item, at Leopardstown when third to Hotazhell in the Irish Champion and at Ascot in the Champion Stakes where he could manage only fifth behind Ombudsman have taken a bit of shine off his reputation.

Benvenuto Cellini, the choice of Ryan Moore in Saturday’s Turf at Keeneland, won the Irish Derby at the Curragh, finished third to Kalpana in the King George VI And Queen Elizabeth Stakes but disappointed in the Prix Niel and the Arc.

Diamond Necklace, set to be ridden against Benvenuto Cellini by Christophe Soumillon, could well turn out to the best of O’Brien’s class of ’26 after landing the Poule d’Essai Des Pouliches, the Prix de Diane, the Nassau Stakes and, from a poor draw, running a blinder behind Daryz in the Arc to finish third.

“Benvenuto won’t go to stud and Diamond is going to stay,” he said.

If much of the attention this weekend will be on the annual American spectacular in Kentucky O’Brien will keep one eye on making sure of a ninth British trainers’ title

He has a lead of just over £175,000 from Andrew Balding but could aim as many as three at the rearranged Group Three Horris Hill Stakes at Newmarket on Saturday, with Bengal Tiger, Accumulation and City Of Gold entered.

O’Brien could also be tripled-handed in the Listed British Stallion Studs EBF Montrose Fillies’ Stakes, with So Lovely, Haven and Speckles all possibles.

He said: “We will probably send a few to Newmarket and they will probably be our last runners except for a Listed race (the Gillies Fillies’ Stakes at Doncaster on November 7) for one of the fillies a week after.”