Experts claim that the philanthropist St Nicholas of Myra is entombed at the 12th century abbey after his body was moved there 800 years ago.
The saint, revered for his extraordinary generosity, lived during the 4th century and was Bishop of Lycia in what is now Turkey.
Due to his habit for leaving anonymous gifts for the poor, he was declared a saint soon after his death in 346, and inspired the legend of Father Christmas.
The bishop was buried in the cathedral church in Myra, which became a pilgrimage site, but Irish historians claim the early crusaders brought his remains back to Jerpoint Abbey.
Philip Lynch, an historian and chairman of Callan Heritage Society in Co Kilkenny, said: “It is an amazing story and yet very few people in Ireland know about St Nicholas’s connection with this country.