Trainer Jessica Harrington has announced the death of Irish Grand National winner Our Duke.
The eight-year-old, who won the Fairyhouse showpiece as a novice last season, suffered a heart attack.
He had endured an interrupted campaign this season after disappointing on his return to action at Down Royal in November.
It was subsequently found he was suffering from a kissing spine, which was treated before he ran better at Leopardstown in February and then went on to land the Red Mills Chase from Presenting Percy.
His last run came in the Cheltenham Gold Cup, buthe did not travel with any fluency and was pulled up.
Harrington tweeted: "We are sad to announce Our Duke died this morning following his usual morning exercise.
"He suffered a massive heart attack. He is a great loss to the Cooper family & our team."
Our Duke won six of his 13 races, amassing nearly £350,000 in career earnings.
Robbie Power was on board for all 11 of his races over jumps and tweeted his own tribute, adding: "Devastated to hear of the passing of Our Duke.
"One of the best I've ever ridden, his performance in last years BoyleSports Irish Grand National will live long in my memory.
"Especially devastating for the Cooper family and his regular work rider @TracyPiggott #whatahorse #legend."