Sinndar, the dual-Derby and Arc de Triomphe winner, was yesterday despatched to his new career at stud. His trainer John Oxx said farewell by declaring the colt had "nothing left to prove."

Sinndar will begin his duties as a stallion at the Aga Khan's Gilltown Stud in Co Kildare for next year at a fee of £30,000. He is the fourth Aga Khan-owned Derby winner to retire at the end of his three-year-old career.

Oxx described Sinndar as "a great horse who never let anyone down, and I will probably never have another one like him."

Nobody has ever had a horse that achieved what Sinndar managed to do this year. Beaten just once in his eight career starts, the son of Grand Lodge is the only horse ever to complete the Epsom Derby/Irish Derby/Arc de Triomphe treble.

He became the first Irish-trained Epsom Derby winner for 16 years when running out a length winner of Britain's premier classic in June and picked up a $1 million (£900,000) bonus when winning the Irish equivalent at the Curragh by nine lengths the following month.

Under jockey John Murtagh, Sinndar then trotted up in the Prix Niel at Longchamp and 11 days ago put the seal on his career when brilliantly triumphing in the Arc.

The Gilltown Stud manager Pat Downes said yesterday: "He is a very exciting addition. There have been a lot of people waiting to hear news and I've no doubt he will be a big hit with breeders."

Oxx said Sinndar should be successful at stud. "He has lovely conformation, a good pedigree, a successful sire line and there was nothing faint-hearted about him. He was the most courageous horse you could wish to see."

The Curragh trainer also poured cold water on suggestions that Sinndar has not fully proved himself because he will not run as a four-year-old. "What those critics don't realise is what a tough test the horse has already been through. From the autumn of a two-year-old career through to the trials, the classics and the autumn of a three-year-old career - there is no tougher test of a thoroughbred than that. That's why the classics have defined the thoroughbred down through the years."