Generous, the champion three-year-old of 1991, has died at the age of 25.
The Paul Cole-trained colt took his three-year-old campaign by storm, winning the Epsom Derby by five lengths, the Irish Derby by three lengths and the King George VI and Queen Elizabeth Stakes by seven lengths.
He stood at Alfred Buller's Scarvagh House Stud in Northern Ireland for over eight years.
"He was unbelievably intelligent for a horse, kind and truly regal," Buller said.
"He will be sadly missed and, to all involved with him, it has been a privilege to have cared for him and looked after him during his last period of life."
Owned by Prince Fahad Salman, the son of Caerleon was ridden to his three major three-year-old victories by Alan Munro, but the partnership ended in defeat in the Prix de l'Arc de Triomphe that October.
Generous was also a top juvenile, springing a 50/1 surprise in the Dewhurst Stakes at Newmarket in October 1990 under Richard Quinn before finishing fourth in the 2000 Guineas on his seasonal return.
Buller said: "He was a special horse. You have never seen a kinder and more likeable animal.
"He got fan-mail and Christmas cards, even up to this year, and the guy who looked after all his fan-mail used to send out wee bits of hair from his tail in a plaque as a souvenir.
"There are other stallions, all of whom were champions in their own way, but there was only one Generous."
Munro said: "I'm very saddened by the news.
"He was a very good horse."Cole said he felt privileged to have been associated with Generous. "It's the end of an era and a sad day for everyone in the Generous clan," said the Wantage handler.
"He was Generous by name, and generous by nature. He was a horse who always gave his all and, if anything, tried a bit too hard.
"He was a very good stayer with sprinter's speed and from a very fast family.
"Trainers hope they can get hold of a very special horse and I'm very lucky to have had Generous."