A son of Hugh O'Neill, Earl of Tyrone, Shane and his family left Ireland in 1607 due to hostility from the English government.

[17][18] He was considered too young to accompany his father on the journey to Rome and was left in Flanders in the care of his elder half-brother Henry.

[23][24] Henry had been a colonel of an Irish regiment in Archduke Albert VII's army, and his death left a vacant colonelcy.

[10] Two weeks after Henry's death, Conry wrote to Philip III, urging him to immediately appoint Eugenio O'Neill, a cousin, to the colonelcy.

[25] In 1604 Spain had signed a peace treaty with England which ended the Anglo-Spanish War, thus Philip III sought to avoid appearing to side with Irish rebels, which could instigate further warfare.

[25] In 1615, Tyrone's chaplain Father Chamberlain arrived in Brussels to arrange a marriage between Shane and the daughter of Mancisador (Secretary for War in the Archduke's government).

The English representative in Flanders, Trumbull, warned his government that the marriage would increase the standing of the exiled Irish community.

[28][29] Hugh's unhappy retainers asked the late earl's secretary to inform Shane that his mother was refusing to give them the money bequeathed to them.

[30] On 16 August 1617,[31][32] Shane's brother Brian was found hanged in his room in Brussels under suspicious circumstances,[17][29] possibly killed by an English assassin.

[36] Shane started using the title El conde de Tyrone around the time he succeeded his half-brother Henry in the command of the Irish regiment in Flanders.

His ascent was recognized by both the Pope Urban VIII and the Infanta Isabella of Spain, the Royal Governor of the Spanish Netherlands.

[21] The title had been granted to his great-grandfather Conn Bacach O'Neill, 1st Earl of Tyrone by Henry VIII of England, and confirmed to his father Hugh by Elizabeth I; it was forfeit by an act of attainder passed by the Irish Parliament in 1608.

(Falkland also claimed that a story was circulating among the Irish that O'Neill had already received a crown of gold, which he kept on a table beside his bed).

[38] O'Neill used his influence with the Pope to have his former tutor Aodh Mac Cathmhaoil (anglicised as Hugh MacCaghwell) installed as Archbishop of Armagh and Primate of All Ireland in 1626.

[39] In 1638, the Irish regiments commanded by O'Neill and O'Donnell were transferred from the Army of Flanders to Spain to bolster forces there in the face of an expected French invasion.

Unfortunately for Constantino, the King, thinking there was no heir, gave the title and command of the Irish regiment to the son of an illegitimate O'Neill cousin.

Constantino went back to Ireland and was an active politician and military officer in the Williamite War as a supporter of King James II.