The 2015 Grand National winner Many Clouds collapsed and died after beating Gold Cup favourite Thistlecrack at Cheltenham on Saturday.
Many Clouds produced a magnificent performance to pip King George VI Chase winner Thistlecrack by a head under Leighton Aspell in the Cotswold Chase, but went down soon after passing the finishing post.
The 10-year-old gelding was attended to by veterinary staff, but was pronounced dead.
Many Clouds' trainer, Oliver Sherwood, said: "What can I say? He gave his all and has left us doing what he loved doing.
"He jumped for fun and was so brave as he has just proved as he really fought like a lion but he has paid the penalty."
Thistlecrack's trainer, Colin Tizzard, told ITV4: "Many Clouds was a fantastic, lovely horse and it's a tragic end to the race - it's as sad as can be.
"There's no question they had a battle, but we were beaten by a better horse on the day. Sadly, it is what happens in our sport occasionally."
Many Clouds won the Hennessy Gold Cup in 2014, but his finest hour came when he won the Grand National at 25-1 the following year.