Ose Partir suffered a fatal injury as Sean and Bernardine Mulryan experienced joy and despair in the same race at Cheltenham.
The Mulryans, until this year sponsors at the Cheltenham Festival through property developer Ballymore, had high hopes of winning the Boodles Juvenile Handicap Hurdle.
The Joseph O’Brien-trained Lark In The Mornin was strongly fancied for the race until heavy rain dented confidence.
The weather had no impact on the outcome after Lark In The Mornin was steered wide of the field by J J Slevin and was produced to deliver his challenge before the last hurdle and won by two lengths at odds of 9-1.
However the owners' second string Ose Partir did not finish the race after being stopped by the fall of another horse.
Officials hunt New Year's Eve revellers who threw beer cans towards race horsesOse Partir, whose trainer Martin Brassil will saddle Fastorslow for the Mulryans in the Cheltenham Gold Cup, was one of two horses brought down by the fall of Karia Des Blaises at the fourth hurdle.
Karia Des Blaises and Mordor, the other who was brought down, got up and galloped back but Ose Partir was fatally injured.
A Cheltenham racecourse spokesperson said: "In the sixth race, Ose Partir sustained an injury and was humanely put to sleep. Our heartfelt condolences are with the connections of both horses.”
RacingTV presenter Nick Luck reported: “Lark In The Morning was the winner of the Boodles’ Fred Winter, owned by Sean and Bernardine. That race for them was truly the best of times and the worst of times, because Ose Partir - who was involved in that pile up on the far side - has suffered a fatal injury.
“The very best of the sport, and the very worst of it for Sean and Bernardine Mulryan. Thoughts with everyone connected to that horse, including the trainer Martin Brassil and all his team.”
Ose Partir's injury came on the same day that Highland Hunter sadly lost his life in the Ultima Handicap Chase. Highland Hunter's passing came just days after he led the procession for jockey Keagan Kirkby.
ITV Racing presenter Ed Chamberlin confirmed the sad news, saying: "I'm afraid it's the news we feared.
"The racecourse have been in touch to say this 'Highland Hunter was immediately attended to by expert veterinary professionals during the third race, the Ultima Handicap, but sadly sustained a fatal injury'. They say 'our heartfelt condolences are with connections' and we echo that."