Two horses - Sir Erec and Invitation Only - suffered fatal injuries on the final day of the Cheltenham Festival.
Gold Cup day began on a sombre note as favourite Sir Erec broke a leg in the opening Triumph Hurdle and had to be put down.
Invitation Only was injured when falling in the Gold Cup which was won by his Willie Mullins-trained stablemate Al Boum Photo.
That was the third horse to die from a total of 498 running at the meeting.
Ballyward suffered fatal injuries in the National Hunt Chase on Tuesday.
Sir Erec, trained in Ireland by Joseph O'Brien for owner JP McManus, was pulled up by jockey Mark Walsh in the race won by 20-1 shot Pentland Hills.
"We're devastated about Sir Erec. Mark said he jumped the hurdle awkwardly and landed awkwardly," said O'Brien.
Winning trainer Nicky Henderson and jockey Nico de Boinville paid tribute to Sir Erec.
"What a gorgeous horse Sir Erec was. Your heart goes out to them," said Henderson.
De Boinville added: "You never like to win a race when that has happened. Thoughts are with Sir Erec's connections."
Retired 20-time champion jockey Sir AP McCoy, who is an adviser to McManus, told ITV Racing: "I'm heartbroken. It is one of the toughest things about the sport."
A raft of new safety measures were brought in for this year's Festival after six horses died at the meeting 12 months ago. A seventh horse later died after suffering injuries at the fixture.
Racing's rulers have been under pressure to improve safety from welfare groups and some politicians.
Sir Erec was sent off as the 11-10 favourite for the Triumph Hurdle after trainer Joseph O'Brien reported that he had recovered from a sore foot last week.
The horse lost a front shoe before the race and the contest was delayed for several minutes as a farrier fitted a new one.
After the injury, Great British Racing chief executive Rod Street said on Twitter: "Oh my word. Standing there as such a gentlemen having his shoe replaced and looking beautiful. Then gone. Poor #SirErec What a low following yesterday's highs."
It was a very different mood to the previous day when Cheltenham was cheered by heartwarming wins for Frodon and Paisley Park.
As part of new measures this year, each of the runners had to undergo veterinary checks before being allowed to race."
David Sykes, director of equine health and welfare at the British Horseracing Authority, told ITV: "There was no reason we could have predicted that injury.
"Beforehand when he was checked, the vets reported he moved well and had no indication of lameness or injuries."
A statement from the BHA added: "We share in the sadness of everyone involved in the sport about the fatal injuries incurred by Ballyward, Sir Erec and Invitation Only this week. Our thoughts are with everyone connected to the horses.
"While the overall injury rate has reduced significantly this year, there will always be an element of risk that can never be entirely eliminated."