Adagio, one of the leading fancies for Saturday's Cesarewitch at Newmarket, died of a heart attack on the gallops on Thursday morning.
The five-year-old had been the subject of a huge gamble in recent weeks with his price coming in from 25-1 into 6-1 second favourite. The horse was trained by David Pipe and was due to have been ridden by Luke Morris, who rode the Prix de l'Arc de Triomphe winner Alpinista last Sunday.
Pipe tweeted this morning: "It is with enormous sadness I have to report that Adagio has suffered a fatal heart attack on the gallops this morning. His owners and everyone at Pond House are beyond heartbroken." #Adagio #FlyHigh
