Multiple Group One winner Azamour was humanely put down at the Aga Khan's Gilltown Stud in Ireland on Saturday.
Trained by John Oxx, the son of Night Shift won the Beresford Stakes as a juvenile before claiming the St James's Palace Stakes at Royal Ascot and Irish Champion Stakes at Leopardstown in his three-year-old career.
Kept in training as a four-year-old, he won the Prince of Wales's Stakes at the Royal meeting when it was run at York and triumphed in the King Georve VI And Queen Elizabeth Stakes which was run that year at Newbury.
He finished his racing career with a third place to Shirocco in the Breeders' Cup Turf of 2005.
A tweet from Aga Khan Studs read: "We are sad to announce that the stallion, Azamour, was put down after sustaining a serious injury in his box this morning.
" Despite the best efforts of both vets and attending staff, the four time Group 1 winner had to be euthanised on humane grounds today."