Trainer William Haggas has paid tribute to Classic-winning filly Sea Of Class who has succumbed to colic.
Last year's Irish Oaks winner underwent surgery after being struck down with the life-threatening illness two weeks ago.
Despite the best possible care, her condition deteriorated on Monday morning.
"She was a marvellous filly and obviously she had a huge amount of ability," Haggas said.
"She was very intelligent and very clever.
"She fought very hard, but today has been a sad day."
Sea Of Class won four races in a row in 2018, culminating in the Yorkshire Oaks, and got within a short neck of catching Enable in the Prix de l'Arc de Triomphe at ParisLongchamp in October.
She ran just once this year, when fifth in the Prince of Wales's Stakes at Royal Ascot on unsuitably soft ground.
Her jockey James Doyle described Sea Of Class as special and said he had been to visit her during her illness.
"I suppose most of all I really enjoyed her win in the Irish Oaks when we came from last to first and just toyed with them," he said. "That was pretty special."