2 horses died while competing at Fork Horse Trials in North Carolina, America at the weekend (5-6 April).
One of the fatalities was a former advanced ride for British rider Rodney Powell.
Conair was being ridden by American rider Will Coleman when they fell at fence 17A on the advanced course.
The 11-year-old gelding got up from the fall and galloped off before being caught and taken back to the stables to be checked by vets.
While he was being examined, he collapsed and died. The cause of his death is still unknown.
Rodney produced the horse to 3-star. Conair was also 2nd at Blenheim CCI 3-star in 2012 with Sir Mark Todd.
Known as Joey at home, Conair was sold to a syndicate last year for Will to ride. Will broke his collarbone in the fall.
The pair came 3rd in the Fair Hill CCI 3-star last year and were aiming for Kentucky 4-star at the end of this month (24-17 April).
Will thanked everyone for their support and kind wishes on his Facebook page.
“Today’s events have been hard for me to swallow, and my sadness is overwhelming me at the moment,” he added.
“I’m truly numb, and will miss the Joey dearly.”
Andrew McConnon’s ride Powderhound also died at the event.
The 15-year-old gelding, who was competing in his first 2-star, collapsed at the stables shortly after showjumping.
“It is hard to find words adequate enough to express the sorrow felt upon the tragic death of a loved horse,” said a spokesman for Andrew.
“This tragedy is once again a reminder that we are so lucky to have horses in our lives, and must appreciate them every moment of every day.”
The event organisers issued a statement after each incident, summarising what had taken place and expressing their heartfelt condolences to the riders.