The skull is allegedly that of St Vitalis of Assisi, an Italian Benedictine monk from the 14th century.
It belonged to an Anglo-Irish family from County Louth, and is housed in a Queen Anne case dating from the 17th century.
There has been no official verification of the claim.
St Vitalis was born in Umbria, Italy, and is said to have lived an immoral and licentious youth.
Story: BBC News | Photo: BBC News