Royal Ascot winner Santiago heads Aidan O'Brien's quest for a 14th success in the Dubai Duty Free Irish Derby at the Curragh on Saturday (live on RTÉ2).

The Authorized colt finished second on his first two starts as a juvenile - including to top-class filly Alpine Star - before getting off the mark at short odds in a maiden at Listowel in September.

Ridden by Ryan Moore at the Royal meeting, O'Brien's charge was a ready winner but is down in trip and up in class this weekend.

"He seems to be in good form since Ascot. He obviously hasn't done much," said O'Brien, who sprang a 33-1 surprise last year with Sovereign.

"He's a horse we always thought would stay and that's why he went to the race in Ascot. It will be interesting coming back to a mile and a half as well.

"I think he's versatile enough ground-wise."

Seamie Heffernan takes over from Moore, with Santiago one of six runners for Ballydoyle.

Among them is Arthur's Kingdom, who is aided by first-time cheekpieces having finished second in the King Edward VII Stakes at Ascot.

"He's in good form as well. Obviously he hasn't done much since Ascot either," said O'Brien.

"He's a real honest, straightforward horse. Ascot was his first run of the year so it was a good run."

Iberia, Dawn Patrol, Tiger Moth and Order Of Australia complete the O'Brien team.

Aidan O'Brien sends a big team to the Curragh

He went on: "Iberia ran well at Leopardstown and he's in good form as well. Probably the better the ground the better it will suit him.

"He's also a straightforward, honest horse. A mile and a quarter is as far as he's gone yet.

"Tiger Moth won nicely over a mile and a quarter the last day on nice ground and seems to be in good form since then.

"We thought Dawn Patrol would stay further than the mile and a quarter and he seems to be in good order since the run, and Order Of Australia is another horse who looks like he might stay further than the mile and a quarter as well."

Regarding the unusual circumstances of the race this year, coming before Epsom for the first time, O'Brien said: "It's the first time all these horses have been over a mile and a half, it's the fairest mile and a half in the world. Horses are going to come from out of the clouds in this race.

"Nobody is going to know what's what until after this race. It's so exciting, it's incredible, really.

"After it we'll know who is the best mile-and-a-half horse, what horses need to drop back to a mile and a quarter or even a mile. That's the best thing about the Curragh, you know where you are going after it, we always think.

"We would usually like two runs well spaced out before the Derby, but most have only had one run. I think it will be the most exciting of all because there's so much mystery in it."

Joseph O'Brien takes on his father with the unbeaten Crossfirehurricane, Galileo Chrome and the filly New York Girl.

It is Crossfirehurricane, ridden by Shane Crosse, who appears his best chance.

"Throughout his whole career he's been progressive, with each run he's taken a big step up with a career-best last time out over 10 furlongs. He earned his spot by winning the Gallinule," said O'Brien.

Sovereign and Padraig Beggy win the 2019 Irish Derby

Last year's Irish Derby winner Sovereign returns to action for the first time since his finest hour in the Comer Group International Vintage Crop Stakes in the final race on Saturday.

The Aidan O'Brien-trained Galileo colt faces seven rivals in the Group Three contest, having last been seen causing a 33-1 upset for Classic glory.

Ridden by Padraig Beggy, Sovereign bowled along at the head of affairs and showed no signs of stopping to beat Investec Derby hero Anthony Van Dyck by six lengths, having been well behind his stablemate at Epsom.

Seamie Heffernan takes over from Beggy in the saddle, and O'Brien said: "He's just ready to start, he's been off a long time. He's done very well but will improve plenty from the run.

"Ideally we might have liked to start a couple of furlongs shorter (than a mile and three-quarters), but the race was there to suit him so we said we'd start and go from there."

He is O'Brien's sole representative, while Joseph O'Brien runs both Master Of Reality and Twilight Payment.

Dermot Weld's Falcon Eight and former Alain de Royer-Dupre inmate Belsanndi, now with Luke Comer whose family sponsor the race, are others of interest.

Kew Gardens has been retired to stud

Meanwhile, Aidan O'Brien's top-class stayer Kew Gardens has been retired to stud.

Winner of the 2018 St Leger at Doncaster, the Galileo five-year-old memorably got the better of Stradivarius in a thrilling finish to the Long Distance Cup at Ascot on British Champions Day last season, his final outing.

Ridden by Ryan Moore, Kew Gardens came out on top by a nose, but unfortunately never got to run again. He retires having won six of 17 races and approaching £1.5million in prize-money.

"Kew Gardens is a big, good-looking horse, clear winded and an excellent mover," O'Brien told the Coolmore website.

"He has super mind and is extremely brave. He was a top-class middle-distance horse."

Kew Gardens will stand under Coolmore's National Hunt banner next season.