Espoir D'Allen, winner of this year's Unibet Champion Hurdle, has been put down following an accident at Gavin Cromwell's stables earlier this month.
The five-year-old took a fall when returning to the yard in County Meath from the gallops and was being treated in Fethard Equine Hospital.
In a statement on Friday, Cromwell said: "It is with great sadness that we have to announce that Espoir D'Allen had to be put down earlier today.
"Following a freak accident two weeks ago, he was relocated to Fethard Equine Hospital. John Halley and his veterinary team deemed that it was inhumane to persist with treatment and, on their advice, we made the tough decision."
Frank Berry, racing manager to owner JP McManus, said: "He was only five and he'd had two fantastic seasons and it's very tough for Gavin and everyone concerned with the horse.
"He gave us some great days."
A surprise 16-1 winner of the Cheltenham showpiece in March, when he was 15 lengths too good for Melon in the hands of Mark Walsh, Espoir D'Allen won eight of his nine starts over hurdles.
In other tragic news to rock the sport, multiple Group One winner Roaring Lion lost his brave fight against colic.
Trained by John Gosden to win the Eclipse, Juddmonte International, Irish Champion Stakes and the Queen Elizabeth II Stakes, the son of Kitten's Joy appeared to be on the road to recovery after twice undergoing surgery for colic in recent weeks.
Roaring Lion produces a brilliant run to beat Saxon Warrior late on in the QIPCO Champion Stakes pic.twitter.com/klAwlviP6a— RTÉ Racing (@RTEracing) September 15, 2018
Owned by Qatar Racing and housed at Tweenhills Stud in Gloucestershire, Roaring Lion covered his first book of mares in the spring, but it was when he was shipped to New Zealand to stand at Cambridge Stud the problem first emerged.