Sir Dermot Ó Seachnasaigh, Chief of the Name, died 1606. He was a son of Sir Ruaidhrí Gilla Dubh Ó Seachnasaigh and Lady Honora O'Brien, daughter of Murrough O'Brien, 1st Earl of Thomond

Murrough O'Brien, 1st Earl of Thomond

Murrough O'Brien, 1st Earl of Thomond was the last King of Thomond.A member of the Irish nobility, he was the son of Turlough O'Brien, King of Thomond and Raghnailt McNamara and also brother of Connor O'Brien, King of Thomond, who was inaugurated King of Thomond in 1528...

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Ó Seachnasaigh was in contention with his elder but illegitimate brother, John Ó Seachnasaigh

John Ó Seachnasaigh

John Ó Seachnasaigh, Chief of the Name, died 1601.Ó Seachnasaigh was the eldest but illegitimate son of Sir Ruaidhrí Gilla Dubh Ó Seachnasaigh. Upon the death of his father, his younger but legitimate half-brother, Sir Dermot Ó Seachnasaigh, inherited Cenél Áeda.Contention between the two brothers...

, who till 1585 claimed lordship of Cenél Áeda. The two brothers travelled to Dublin to attended the 1585 Parliament, after which no more is heard of John till 1601.

Sir Dermot married Shyly Ni Hubert, and had issue Roger Gilla Dubh (born 1583), Dathi, William, Joan, Julia and Honora.

• William had sons William, Edmond, Roger and Dermot.
• Joan married Sir William Burke, and was the mother of Richard Burke, 6th Earl of Clanricarde
  Richard Burke, 6th Earl of Clanricarde
  Richard Burke, 6th Earl of Clanricarde, Irish peer, died August 1666.Richard was a first cousin to the previous Earl and had served under him in the royalist forces during the Irish Confederate Wars. When restored, the Clanricarde estates were heavily in debt and a great deal of litigation was...
  
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• Julia married Teige O'Kelly of Gallagh.
• Honora married Johnock Burke of Tully.