The actor and his wife Carlyn welcomed a granddaughter last week (beg18Aug14) but it is not known which of their two sons, Padraig and Conor, fathered the new addition to the family.
In a series of posts on Twitter.com, Duffy writes, "I'm a gramps again! For the 4th time!! Everyone fine and healthy!! Btw (by the way) it's a grand daughter!"