Neighbouring the Clandeboye to the north-east were a group of Highland Scots in the Glens of Antrim. They were Gallowglass soldiers under the leadership of the MacDonnell of Antrim who had established themselves by the mid-16th century as Lords of the Glens (the remaining parts of the area which Normans had previously held as the Earldom of Ulster). During a conflict with them, the heir to Clandeboye, Niall O'Neill (son of Hugh O'Neill) was killed in 1537, weakening the natural succession. To the west of Clandeboye were their more powerful O'Neill kinsmen, the O'Neills of Tyrone (from whom the Clandeboye's had branched off in the 13th century). During the Tudor conquest of Ireland under Henry VIII, whereby the English were attempting to establish the Kingdom of Ireland, various Gaelic kings were offered a policy of surrender and regrant. They could keep their traditional territories as lords, so long as they legally and culturally Anglicised, joined the Anglican Church and pledged allegiance to Henry VIII: Conn Bacach O'Neill took him up on the offer, exchanging the Kingship of Tyrone for the Earldom of Tyrone in 1542. The heir to this title was the Baron Dungannon: Conn Bacach's son Shane O'Neill was overlooked and the title went instead to Shane's illegitimate alleged half-brother Matthew O'Neill. During the 1550s and 1560s, Shane (later known as "the Proud") arose to assert his rights, protesting to Elizabeth I and infilicted notable military defeats on establishment figures such as the Earl of Essex. The O'Neills of Clandeboye diligently offered their services up to the Crown forces during the campaign of Shane O'Neill. Part of the backstory of this was that Brian Faghartach O'Neill (the oldest son of the aforementioned Niall Oge O'Neill) was assassinated by a then 20-year-old Shane O'Neill in 1548. Brian Faghartach was the first Lord of Upper Clandeboye, thought likely to be involved in a surrender and regrant, allowing him to establish himself as a Lord of a portion in the now split up Clandeboye. When Shane rose up, he was able to establish his influence over Clandeboye and force it into being one of his urriaght (subsidiary) territories. At Carrickfergus, an Anglo-Irish crown garrison had been established under William Piers with the support of Brian McPhelim O'Neill, the Lord of Lower Clandeboye, who was subsequently knighted for supporting them against Shane the Proud and also the Scots in the Glens of Antrim.