The favourite for the race had to be put down moments after the JCB Triumph Hurdle at the Cheltenham Festival – the second fatality of the week after Ballyward on day one.
The horse snapped its leg in horrifying scenes on the course, and news of its death was confirmed just moments later.
Reports though have suggested that Sir Erec, who had struggled with his shoes in the minutes before the race, was already injured.
And PETA (People for the Ethical Treatment of Animals) have slammed the decision to allow the colt to race in the first place.
“Sir Erec – who, according to reports, was already suffering from a leg injury prior to the race – is the latest horse to lose his life in this racing season’s carnage,” a statement from Mimi Bekhechi, Director of International Programmes at PETA read.
“Authorities must urgently investigate how he was cleared to race and whether he was on medication that masked an injury – and if so, file cruelty charges quickly.
“How many more horse deaths is it going to take before we put the abusive horse-racing industry out to pasture?”
A number of new safety measures had been brought in for this year’s Cheltenham Festival after seven horses died last year.
READ MORE: AP MCCOY LEADS TRIBUTES TO SIR EREC
Every runner at the event now has a veterinary check before racing for the first time.
Inexperienced jockeys are also being told they must walk the course before riding at the meeting.
And director of equine health and welfare at the British Horseracing Authority David Sykes denied Sir Erec had gone into the race injured.
He said: “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.”
Sir Erec’s trainer Nicky Henderson paid tribute moments after its death and said: ”What a gorgeous horse Sir Erec was. Your heart goes out to them.
“We’re all a family and JP [McManus, owner] is a big part of our team.
“He’s one of the great men of national hunt racing. That was not fair at all.”
A statement from the Cheltenham course added: “As animal lovers, we hate to lose any horse and of course we shall review the incident.”