The League Against Cruel Sports charity said the death brings the total at Cheltenham Festival to 81 horses since 2000.
The race was set to be Envoi Allen’s last, with its owners Cheveley Park Stud previously confirming he would retire.
He was considered a legend by fans of the sport, having won three times at Cheltenham. He was also a 10-time Grade 1 winner.
Emma Slawinski, chief executive at the League Against Cruel Sports, said: “A third horse death in only four days is heartbreaking news but not a surprise – every year horses are raced to their deaths at the Cheltenham Festival.
“Since the turn of the century, the death toll of horses that have died at the festival has reached 81, which is simply shocking.
“There would be a huge outcry if this death toll happened in any other sport, so we need to start prioritising horse welfare.”
