Background
O'Brien was the son of Barnabas O'Brien, 6th Earl of Thomond and Anne Fermor.
O'Brien was the son of Barnabas O'Brien, 6th Earl of Thomond and Anne Fermor.
Henry, Lord Ibrackan (c1643-1678)
This made O'Brian a brother-in-law of Henry Cromwell, who had married Sarah's sister Elizabeth. O'Brian and Sarah had five children:
Henry, died in infancy
Henry Horatio, Lord Ibrackan (d 1690), who was father of Henry O'Brien, 8th Earl of Thomond (1688–1741)
Elizabeth (d 3 June 1688), without issue
Auberie Anne Penelope, married Henry Howard, 6th Earl of Suffolk and had issue
Mary, married Sir Matthew Dudley, 2nd Baronet.