Ed Dunlop said the death of Red Cadeaux was his "saddest day in racing".
The globetrotting nine-year-old had to be put down due to "irreversible" complications following surgery on a leg injury sustained during the Melbourne Cup at Flemington.
"This is my saddest day in racing," Dunlop said in a statement. "Red Cadeaux was a much-loved member of our family and my thoughts are with his owner Mr (Ronnie) Arculli and my staff, particularly Robin Trevor-Jones and Steve Nicholson, who spent every day caring for this horse.
"Unfortunately the complication was irreversible and the decision to euthanize the horse, whilst terribly hard, was made in his best interests.
"Red Cadeaux has given us and the racing public so much joy competing with great distinction across the world. He was an incredibly tough competitor with a wonderful nature and he will be dearly missed by all.
"I want to thank all the vets in Australia, particularly at the University of Melbourne Equine Clinic, that have worked tirelessly on the horse since the race and given him the very best of care.
"On behalf of Mr Arculli and my staff, I also want to thank the Australian public and his racing fans around the world for their wonderful support and well wishes during what has been an incredibly tough time for us all."
Running in the Melbourne Cup for a fifth time, having finished second in it three times, the nine-year-old was pulled up by Gerald Mosse in the closing stages after fracturing the medial sesamoid in his left-fore fetlock.
His racing career was over, but it had been hoped he would recover from the emergency surgery.
Red Cadeaux's final resting place will be at Flemington Racecourse.
Arculli said: "For a race that stops a nation we were lucky to have a horse that touched a nation. We will miss Red Cadeaux dearly."
Red Cadeaux earned just under £5m in prize-money, winning seven races - including the 2012 Hong Kong Vase at Sha Tin.
