Sea The Stars was retired Tuesday after becoming the first horse to complete a sweep of three top European races in the same season.
The 3-year-old Irish colt's victory in the Prix de l'Arc de Triomphe this month followed triumphs in the English 2000 Guineas and Derby to make it six Group One wins in a row.
"We feel it is unfair to keep him going any further given his unprecedented record of achievement in the last six months," trainer John Oxx said. "He's come out of the Prix de l'Arc de Triomphe in his usual good form. He is fit and healthy and has been cantering since the race."
Oxx said he has no details on his stud career.
During two years on the track, Sea The Stars lost just one of his nine races _ in his debut _ and earned around $7 million in prize money.
The retirement was made after discussions with owner Christopher Tsui. It denies Sea The Stars the chance for a final triumph at the Breeders' Cup Classic on Nov. 7.
"He's had a long season and has been in regular fast work from March 3, with his final workout on October 2," Oxx said. "He's been in intensive training for seven months with only a three-week break after the Eclipse Stakes at the beginning of July."