Sea Of Class has had her racing career ended by a serious bout of colic.
The Irish and Yorkshire Oaks winner was struck down on Wednesday and is receiving round the clock attention.
Her condition is so grave that her trainer William Haggas was unequivocal that her days on the track are over.
“It’s devastating news. She had surgery on Wednesday and is under intensive care,” said Haggas.
“If she was a human you would say she was critical but stable, that’s how it is, there’s nothing more I can add really. You just have to take each day as it comes.
“There is no question that her racing career is over, 100 per cent.”
After gaining her Group One wins at the Curragh and York, Sea Of Class came closer than anyone to ending Enable’s winning streak when pushing her all the way in last year’s Prix de l’Arc de Triomphe.
Her sole start this year came at Royal Ascot in the Prince of Wales’s Stakes when she finished fifth on unfavourable soft ground.
Her regular rider James Doyle labelled her as one of the best horses he has ridden.
“It’s devastating, not nice at all, but as tough as it is for me, it’s tougher for those who see her every day – William and Maureen and not least her owners,” Doyle told Sky Sports Racing.
“Let’s hope she can bounce back from it and at least go to stud one day.
“She was without doubt the best filly I’ve ridden, probably one of the best I’ll ever ride. She had a devastating turn of foot. It’s heart-wrenching.”