The skull, which had two bullet holes in the front of the head, was found in a sack in the bottom of a ditch at Tralee, County Kerry.

Tommy Foley with the skull

Shergar, a winner of the British and Irish Derbys, was kidnapped by the IRA in 1983, two years after being retired.

Des Leadon, head of the Equine Centre's clinical pathology department, said: "We know that Shergar was at least five years of age at the time he was kidnapped, but this horse died somewhere about two years of age."

"This could not therefore be the skull of Shergar and we do not need to proceed any further or carry out any further laboratory tests."

The man who found the skull, local councillor Tommy Foley, has spoken of his regret at the news.

Mystery

"I would not dispute the findings of the experts, but I am very disappointed," he said.

"I was more or less positive it was Shergar because of the County Kerry link with the abduction.

"I would still wish that Shergar would be found eventually to lay the mystery to rest once and for all. I am sure I share that with everyone who loves racing."

The skull was originally taken by Gardai to Naas police station in County Kildare, where the abduction was first investigated 17 years ago, before being transferred to the Equine Centre.

Shergar

Won: Guardian Newspapers Classic Trial Chester Vase Derby Stakes Irish Sweeps Derby King George VI and Queen Elizabeth Diamond Stakes Winnings: �436,000 Retired: September 1981

Shergar was taken from the Ballymany Stud in County Kildare, where he had embarked upon his new career as one of the most valuable stallions in the world.

He was abducted at night along with his groom, who was held at gunpoint in the horse van before being released 20 miles away.

Negotiations with the kidnappers continued for four days and a Polaroid photograph was provided showing Shergar with an up-to-date copy of the Irish Times before the kidnappers suddenly fell silent.

The kidnapping became one of the great mysteries of the 1980s, with constant reports of sightings, but despite a nationwide search no trace of him was ever found.

Informer

Insurers refused to pay out without proof of the horse's death.

Former IRA informer Sean O'Callaghan, who is from Co Kerry, later claimed that the horse had been killed by his abductors who were unable to handle him.

O'Callaghan, a convicted murderer who turned police informer, said the paramilitary group had demanded a �5m ransom.