The rest of the earl's life was mainly occupied by endeavours to maintain his influence, and by an undying feud with his son Shane (John), arising out of his transaction with Henry VIII.
For not only did the nomination of O'Neill's reputed son Matthew as his heir with the title of baron of Dungannon by the English king conflict with the Irish custom of tanistry which regulated the chieftainship of the Irish clans, but Matthew, if indeed he was O'Neill's son at all, was illegitimate; while Shane, Conn's eldest legitimate son, was not the man to submit tamely to any invasion of his rights.
The fierce family feud only terminated when Matthew was murdered by agents of Shane in 1J58; Conn dying about a year later.
Conn was twice married, Shane being the son of his first wife, a daughter of Hugh Boy O'Neill of Clanaboy.
Shane O'Neill (C. 1530-1567) was a chieftain whose support was worth gaining by the English even during his father's lifetime; but rejecting overtures from the earl of Sussex, the lord deputy, Shane refused to help the English against the Scottish settlers on the coast of Antrim, allying himself instead with the MacDonnells, the most powerful of these immigrants.
Nevertheless Queen Elizabeth, on succeeding to the English throne, was disposed to come to terms with Shane, who after his father's death was de facto chief of the formidable O'Neill clan.
Baron of Dungannon, if Shane would submit to her authority and that of her deputy.
Elizabeth was less concerned with the respective claims of Brian and Shane, the one resting on an English patent and the other on the Celtic custom, than with the question of policy involved in supporting or rejecting the demands of her proud suppliant.
There were at this time three powerful contemporary members of the O'Neill family in Ireland - Shane, Turlough and Hugh, 2nd earl of Tyrone.
Elizabeth at last authorized Sussex to take the field against Shane, but two several expeditions failed to accomplish anything except some depredation in O'Neill's country.
Sussex had tried in 1561 to procure Shane's assassination, and Shane now laid the whole blame for his lawless conduct on the lord deputy's repeated alleged attempts on his life.
This victory greatly strengthened Shane O'Neill's position, and Sir Henry Sidney, who became lord deputy in 1566, declared to the earl of Leicester that Lucifer himself was not more puffed up with pride and ambition than O'Neill.
In his private character Shane O'Neill was a brutal, uneducated savage.
He was brought up in London, but returned to Ireland in 1567 after the death of Shane, under the protection of Sir Henry Sidney.
Taylor, Owen Roe O'Neill (London, 1896); John Mitchell, Life and Times of Hugh, Earl of Tyrone, with an Account of his Predecessors, Con, Shane, Turlough (Dublin, 1846); L.
Armagh itself fell before the king Brian Boroime, who was buried here; and before Edward Bruce in 1315, while previous to the English war after the Reformation, it had witnessed the struggles of Shane O'Neill (1564).
His first wife, Joan O'Reilly, was the mother of Calvagh, and two daughters, both of whom married O'Neills; the younger, Margaret, was wife of the famous rebel Shane O'Neill.
Hugh then appealed to Shane O'Neill, who invaded Tyrconnel at the head of a large army in 1557, desiring to make himself supreme throughout Ulster, and encamped on the shore of Lough Swilly.
Calvagh was then recognized by the English government as lord of Tyrconnel; but in 1561 he and his wife were captured by Shane O'Neill in the monastery of Kildonnell.
His wife, Catherine Maclean, who had previously been the wife of the earl of Argyll, was kept by Shane O'Neill as his mistress and bore him several children, though grossly ill-treated by her savage captor; Calvagh himself was subjected to atrocious torture"during the three years that he remained O'Neill's prisoner.
Calvagh, however, died in the same year, and as his son Conn was a prisoner in the hands of Shane O'Neill, his half-brother Hugh MacManus was inaugurated The O'Donnell in his place.
Hugh, who in the family feud with Calvagh had allied himself with O'Neill, now turned round and combined with the English to crush the hereditary enemy of his family; and in 1567 he utterly routed Shane at Letterkenny with the loss of 1300 men, compelling him to seek refuge with the MacDonnells of Antrim, by whom he was treacherously put to death.