Brénainn mac Ferguso

https://en.m.wikipedia.org/wiki/Baith%C3%A9ne_mac_Br%C3%A9naind

Baithéne was the son of Brénainn mac Ferguso, who was the brother of the father of St Columba , making Baithéne a first cousin of Columba. Both he and Columba were great-grandchildren of Niall of the nine hostages, and were born into the family of Cenél Conaill branch of the Northern Uí Néill. They were thus both part of one of the ruling families of Ulster.[2]