Many Clouds died of a pulmonary haemorrhage, a post mortem has confirmed.

The racing superstar sadly died minutes after beating Thistlecrack in the Cotswold Chase on Cheltenham Festival Trials day (Saturday, 28 January).

While the 2015 Grand National winner had shown signs of post-race ataxia in the past — characterised by a loss of balance in walking following exercise — he did not show any signs of this following Saturday’s race. The post-mortem has also ruled this was in no way linked to his death.

The British Horseracing Authority (BHA) initiated the post mortem, with permission from owner Trevor Hemmings and trainer Oliver Sherwood. It was carried out by Veterinary Investigation Services and a member of Three Counties Equine Hospital also attended.

A statement from the BHA said the horse sustained a “severe pulmonary haemorrhage”, which was the cause of his death.

“Many Clouds received immediate care and attention from the team of racecourse vets, but they were unable to save the horse,” added the BHA spokesman.

“No significant underlying health issues were discovered in the autopsy.”

This cause of death in racehorses is rare (0.048% of runners in jump racing) and the overall fatality rate within British racing has dropped by a third in the last 20 years.

“Episodes such as this are rare, and can occur in horses which have no underlying health issues, and amongst all disciplines of sport horses,” said Tony Welsh, BHA’s acting chief veterinary officer.

“In spite of the rarity of these incidents, as a sport we are determined to do more to understand what causes these symptoms, and whether more can be done to prevent it.”

He added several studies have been commissioned as part of the £32 million-plus invested in veterinary science and research by the sport though the Horserace Betting Levy Board since 2000.

Many Clouds wore a heart-rate monitor in training on 17 November 2016. The data collected at that time was within normal parameters for both his heart rate during exercise and his recovery rate.

“Post-race ataxia and similar signs are linked to an increase in body temperature after exercise and can be treated by providing the horse with water,” added Mr Welsh.

“It is not uncommon in racehorses or other sport horses.

“Despite some reports following the incident, there is no existing veterinary evidence which links these symptoms with racehorse fatalities, and the post-mortem results have categorically proved that the signs exhibited by Many Clouds in the past were in no way present or associated with his sad death at Cheltenham.

“Our thoughts remain with everyone connected to the horse. Any loss of life is regrettable, and we continue to use research, safety measures, regulation and education to reduce fatality rates to as close to zero as possible.”

Tributes to a racing great

“Let’s enjoy the life of Many Clouds — he was a real wonder horse,” said trainer Oliver Sherwood. “He had guts and jumping ability — with that you will always win races.”

He added that he “died doing what he loved — he loved jumping and he loved racing”.

“I have always told everyone, he would die for you and he has gone and died for us, doing what he loved,” he said.

“It happens to us all, we all go at some point. He has gone out on a high.”

Bought by Trevor Hemmings as a three-year-old for €6,000 (£4,700), Many Clouds was the youngest horse to win the National (aged eight) since Bindaree in 2002.

Affectionately known at home as “black aeroplane” — a name also used by racing fans for Sprinter Sacre — Many Clouds had a fan club, members of which regularly sent him letters, carrots, apples and polos.

“Horses like Many Clouds don’t grow on trees and it is going to be difficult to find a replacement,” added Sherwood.

“I have to enjoy the Hennessy and National wins and it was probably a career-best from him today.

“It is very sad for everyone — CJ (Chris Jerdin) who looks after him at home, Lisa my travelling head girl, Stefan, my head man and all the team at Rhonehurst.

“It was spine-chilling walking back down when it was announced and the whole crowd clapped. That finished me completely and I did lose it a bit then.”

Jockey Leighton Aspell told The Times today that it was “a privilege to have been part of such a wonderful partnership”.

Meanwhile Nathan Horrocks, Many Clouds’ work rider, added it is “a massive loss to everybody”.

“He wasn’t just of huge importance to the yard, he was of huge importance to Lambourn and the sport,” said Horrocks.

“Honestly, you can’t believe the amount of people that come up to us and say ‘I hope the horse is well and we are looking forward to him running’. He has really captured the nation.

“It’s devastating for all the team losing Clouds, I’m deeply saddened for poor CJ, he truly lived every day for Clouds and I’m going to miss our conversations of Clouds’ future successes.

“A special thanks to his owner Mr Hemmings, for his passion for this amazing sport and bringing clouds into our lives.”

Chris Jerdin said it broke his heart. “He wanted for nothing and meant everything to me,” he added in his column for Monday’s Racing Post.

Colin Tizzard, Tom Scudamore and AP McCoy are among the many others to honour the racehorse.

Tania Kindersley’s moving tributes, on her The Red Mare Facebook page, have been shared thousands of times across social media.

“As I go down in the rain to settle my own fragile thoroughbreds for the night, I find myself weeping for a horse I never met,” she said.

“I gentle the mares and speak mournful words to them and scratch them in their sweet spots, in the places that make them close their eyes with delight. ‘Don’t you go,’ I say to them, fiercely. They nod their heads at me as if to say: not for a while yet.

“One day they will go. Everybody who loves horses and keeps horses and cares for horses has the thought, like a fleeting shadow in the back of the mind, that one day there will be an empty box or an empty field.

“They are not given, these magnificent creatures, they are only lent, on borrowed time.

“Some will go quickly, in their pomp, as Clouds did today; some will go slowly, as the twilight of age closes in.

“Somehow, in their mysterious, magical equine way, they consent to live for a short time with the humans to whom they give so much joy.”