Group One winning stayer Brown Panther has suffered a fatal injury in his defence of the Irish St Leger at the Curragh.

Eighth in the 2013 Melbourne Cup, Brown Panther was also entered for this year's race.

All seemed to be going to plan as he sat in second tracking the pace, but he was suddenly pulled up by Richard Kingscote at the halfway point having suffered a broken hind leg.

His breeder and part-owner, former England striker Michael Owen, described the incident as the saddest day of his life.

"It's the saddest day of my life. The toughest, most honest, brilliant horse I will ever set eyes on passed away today doing the thing he loved the most," Owen said on Twitter.

"A shattered hind leg that was irreparable according to the first class team at the Curragh ended his life.

"I was with him when he was born, shared an experience for seven years that will never be repeated and gave him his last kiss goodbye.

"What an honour to own and breed him. I love you Panther, life will not be the same without you."

Paul Hensey, general manager at the Curragh, said the horse could not be saved.

"Brown Panther suffered a compound fracture of his hind leg. There were three vets with him within seconds and he was put down as unfortunately he just couldn't be saved," he said.

One of Brown Panther's greatest moments came at Royal Ascot in the 2011 King George V Stakes, a win which left Owen visibly moved.

Successful in the Dubai Gold Cup in March, other career highlights included the Goodwood Cup of 2013 and the Ormonde Stakes at Chester.