The descendants of Niall spread over Ireland and became divided into two main branches, the northern and the southern Hy Neill, to one or other of which nearly all the high-kings (ard-ri) of Ireland from the 5th to the 12th century belonged; the descendants of Eoghan being the chief of the northern Hy Neill.'
O'Neill, grandson of Neill, or Niall, the name O'Neill becoming about this time an hereditary family surname 2), whose grandson, Flaherty, became renowned for piety by going on a pilgrimage to Rome in 1030.
Contemporary with him was Neill Mor O'Neill (see below), lord of Clanaboy, from whose son Brian was descended the branch of the O'Neills who, settling in Portugal in the 18th century, became prominent among the Portuguese nobility, and who at the present day are the representatives in the male line of the ancient Irish kings of the house of O'Neill.
The Clanaboy (or Clandeboye) branch of the O'Neills descended from the ancient kings through Neill Mor O'Neill, lord of Clanaboy in the time of Henry VIII., ancestor (as mentioned above) of the Portuguese O'Neills.
Neill Mor's great-greatgrandson, Henry O'Neill, was created baronet of Killeleagh in 1666.
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