Six-time group one winner Vengeance of Rain.
The six-time group one winner suffered a heart defibrillation during Saturday's Centenary Vase at Sha Tin and was pulled out of the race.
It was the second time the complaint had surfaced and under Hong Kong rules, Vengeance of Rain (Zabeel x Danelagh by Danehill) would not have been permitted to start for six months.
Trainer David Ferraris and the Chow family which owns the gelding decided immediately he should be retired.
"It's heartbreaking, but I guess in racing you have to roll with the punches," said Ferraris.
"He has been training like a bomb, there was never any indication ... so it's such a shock for this to happen."
"Without a doubt he is the best horse I've ever trained."
Vengeance of Rain's first heart irregularity happened two years ago but after a spell at Cambridge he returned to his best form and became the first Hong Kong-trained horse to win at the World Cup meeting in Dubai where he claimed the group one Sheema Classic.
Vengeance of Rain was last season crowned Hong Kong's Horse of the Year as well as champion stayer and most popular horse. With earnings of $NZ12 million, he is the highest stakes earner in Hong Kong history.
He was bought at Karaka in 2002 by Graeme Rogerson for $300,000, and raced under the name Subscribe for Lloyd Williams in Australia.