Godolphin’s 2018 National Stakes winner Quorto suffered a fatal injury on the gallops on Thursday.
The Dubawi colt was only seen three times on a racecourse, but won on each occasion.
A debut victory at Newmarket was followed by an impressive success in the Superlative Stakes back at Headquarters.
He then went to Ireland for the National Stakes, where he beat subsequent Derby winner Anthony Van Dyck in what was to be his final start.
A setback ruled him out of the 2019 campaign, but he had returned to training with Charlie Appleby this term.
Appleby told www.godolphin.com: “Quorto was a very talented colt who was absolutely brilliant when winning the National Stakes.
“It is a great shame that we did not get to see him on the racecourse again and he will be sorely missed by all the team at Moulton Paddocks.”