Cheltenham Gold Cup hero Synchronised suffered a fatal injury in the John Smith's Grand National at Aintree.
The Jonjo O'Neill-trained gelding was given a superb ride by multiple champion jockey Tony McCoy to win the blue riband at Prestbury Park last month, and was bidding to become the first horse to complete the double since the legendary Golden Miller in 1934.
McCoy was unshipped by the nine-year-old before the start of the race, with Synchronised running loose before being caught and reunited with his rider.
But his race was not to last long as he made it only as far as Becher's Brook, the sixth fence, running on riderless afterwards, and it was revealed shortly after the race finished that he had lost his life.
McCoy gave up his one remaining ride in the concluding bumper.
There was a second fatality in the race, with the Malcolm Jefferson-trained According To Pete, who was brought down at Becher's on the second circuit, also put down.
Aintree managing director Julian Thick said: "We are desperately sad at these two accidents and our sympathies are with the connections of both horses.
"When a horse gets hurt, everyone is deeply upset. Safety is the first priority for the organisers of the Grand National and we make every effort to ensure that everyone involved in the event is able to participate in safety.
"Horseracing is a sport that is very carefully regulated and monitored by the British Horseracing Authority, but risk can never be completely removed.
"All horses and riders in the Grand National have to meet very high standards set by an independent panel of experts.
"The Grand National is a professional and well-organised race. Only the best horses and the best jockeys are allowed to enter.
"Since last year's race we have made further significant chances to the course and there have been four races run over the course without serious incident since then.
"After today, we will, as always, be looking at all aspects of this year's race to see how we can improve safety further.
"We work closely with animal welfare organisations, such as the RSPCA and World Horse Welfare, to make sure we are up to date with the latest thinking and research regarding welfare and safety."
Professor Tim Morris, Director of Equine Science and Welfare for the British Horseracing Authority, said: "We are very sad about the fatal injuries suffered by Synchronised and According to Pete in the Grand National.
"In both cases the horse incurred a fracture to the leg and the humane option was to put the injured horses down.
"The Grand National undoubtedly represents a challenge to both horse and rider.
"It has inherent risks, but, working closely with Aintree and other stakeholders, we do all we can to minimise these risks while maintaining the unique character of the race.
"We will examine closely the circumstances which led to both incidents.
"The key data from these accidents will be collated, as is the BHA's policy in the event of any serious equine injury.
"Each year the BHA and Aintree review all incidents which occur during the Grand National meeting and consider what measures can be taken to address the risk of a repeat in the future.
"The BHA takes its responsibility of looking after the welfare of horse and rider very seriously.
"We consult and work with recognised welfare organisations such as the RSPCA, SSPCA and World Horse Welfare. It is our stated objective to continue to reduce the number of injuries and fatalities which occur in racing."
RSPCA equine consultant David Muir insisted the race needs to come under further scrutiny.
He said: "We can't support the Grand National unless they react to issues of the particular race, how much can you modify it?
"It is the risk factor which needs looking at. Why can we not raise the number of finishers?
"I don't think we should ban the Grand National, but there are elements of it which cause problems and we should deal with these.
"We've always had concerns about drop fences (like Becher's Brook) and we'd look to reduce the risk factor.
"We'd love to see 40 finishers. The Grand National is a work in progress and we think we can get more finishers and a safer race."
World Horse Welfare chief executive Roly Owers said: "The deaths of Synchronised and According to Pete are a terrible tragedy and our thoughts go out to everyone connected with these horses who will clearly be devastated.
"Over the coming days it will be important to establish the facts. There is no doubt that questions need to be asked and that is exactly what we'll be doing.
"We won't know what if any changes will need to be made until we know the exact circumstances of their falls. It's hugely important to us that everything possible is being done to protect the safety of the horses and riders.
"No race, especially the Grand National, can be without risks but there is a balance between acceptable and unacceptable risk and we need to strive to get that balance right."
