The dig for of the remains of Red Hugh O'Donnell could be over after archaeologists discovered a skull and bones in the exact chamber identified as his burial site.
The Irish historical hero's dying wish in September 1602, was to be buried in the Chapel of Wonders, at a Franciscan monastery in Valladolid in northwest Spain.
Today, after a week-long excavation of a site on Constitution Street archaeologists have uncovered two coffins and at least one set of remains.
The other coffin could be the original one which held the remains of explorer Christopher Columbus who was reinterned to Seville Cathedral.
The Mayor of Valladolid Óscar Puente tweeted a photograph showing the excavated site with a human skull and long bones- believed to legs.
He wrote: "In the chapel of Wonders, in the exact place where Red Hugh O'Donnell is believed to have been buried as well as Christopher Columbus, some remains and two coffins have appeared."
Historian Hiram Morgan, a UCC academic, said the discovery is fascinating and explained O'Donnell's remains should be easily identifiable - as he had no big toes.
O'Donnell, who was one of the masterminds the Nine Years War from 1593 to 1603, suffered frostbite while hiding in the Wicklow mountains following a daring escape from Dublin Castle.
Morgan also said if the discovery turns out to be O'Donnell, it could bring answers to the mystery surrounding his death or possible murder.
"Nothing is certain until they do DNA, but his lack of big toes could certainly point the way.
"Also, if they identify his bones, then they could do tests to discover why he might have died.
"What disease he had or whether he was poisoned or had a parasite. "That would lay all that to rest. It's fascinating, and it would be brilliant if it turns out to be him.
Along with his father-in-law Hugh O'Neill, Earl of Tyrone, Red Hugh led arguably one of Ireland's most successful rebellions against the English in history.
Red Hugh, an Irish nobleman, of the Donegal O'Donnell dynasty, died in Spain aged 29 while trying to secure a second wave of support from the Spanish against their shared enemy, England.
After suffering defeat during the Siege of Kinsale, Red Hugh travelled to Spain to seek further support from King Philip III, but he died before he could.
It is believed he contracted an infection, or according to others, he was poisoned by British spy James Blake, a merchant sailor from Galway.
Blake claimed he had assassinated Reg Hugh on behalf of the Governor of Munster, George Carew.
But historian Morgan said it is generally considered Blake claimed this just to "get some kind of benefit from Red Hugh's death."
"He claimed he poisoned him, but there is no proof of that really."
Interesting Morgan has revealed there is another Irishman buried in the same graveyard in Valladolid.
"Somewhere beside Red Hugh O'Donnell is another Irishman William Burke, he was a contemporary of Red Hugh.
Red Hugh made his chief of the Burke's of Mayo. But they both had to flee to Spain. He is buried in the same church, somewhere near Hugh. He survived in Spain longer than Red Hugh. Two for the price of one you could say. Or three if you count Columbus."
Red Hugh led a colourful life, and his backstory has fascinated historians for centuries.
Morgan believes the interest in Red Hugh is not surprising, as he was a classic hero.
He says: "He was one of these Irish heroes who tried and very nearly succeeded, and he also has this great backstory.
"He was captured by the British and managed to escape."
The English used a ship loaded with beer and wine as a ruse to capture Red Hugh.
They sailed it up the coast to Lough Swilly, pulling in to harbour near Rathmullan.
They pretended to be merchants selling the wine and beer and managed to draw the young Hugh on board.
He was captured, and as the O'Donnells had no boats to attempt a rescue, they could only watch as the ship sailed back around the coast to Dublin, where Red Hugh was imprisoned.
Morgan explained: "His father-in-law, Hugh O'Neill, and others arranged his escape, and that was when he had to hide in the mountains.
"When he got back to Donegal about a month later, they had to amputate his big toes.
While Red Hugh O'Donnell fought and won many battles against the British and his bravery won the hearts of a nation, his love life was less successful.
He married Rose O'Neill, the daughter of his ally Hugh O'Neill, the Earl of Tyrone.
The partnership was an unhappy one that never produced a child.
Red Hugh tried twice to end the marriage before he eventually left for the ill-fated trip to Spain