In 1567 the fortress was gallantly defended against a fierce attack made by the great Shane O’Neill, and he was successfully repulsed. The strength of the White family gradually decreased, and in 1590 they could only muster a hundred and twenty foot soldiers and twenty horsemen to defend their lands, while eight years later twenty footmen was the total of their fighting strength.
The M’Artans and O’Neills joined together and dispossessed them, the former family taking possession of Killyleagh. Their estates were, however, forfeited at the close of the sixteenth century for the part they took in the rebellion of the Northern Earls, and some time after this the lands were granted to the Hamiltons.
General Monk partly demolished the castle in 1649, and the Hamiltons began to rebuild it in 1666.
James I. had created the head of the family Earl of Clanbrassil and Viscount Clandeboye, but the last to hold the title died in 1676. It is said he was poisoned by his wife, Lady Alice of Clanbrassil, a daughter of the Earl of Drogheda, who was a beautiful and vicious woman, and after plunging the estate into debt desired to contract a wealthy marriage.
At this time the Earl’s mother, Lady Anne, resided at Killyleagh Castle in accordance with the wishes of her husband’s will.
As Earl Henry left no children the estate was divided amongst his cousins, Killyleagh falling to the lot of James Hamilton. When James died in 1683 his lands were divided between his brother Gawin, ancestor of the present Colonel Rowan-Hamilton, D.L., of Killyleagh Castle, and his daughter Anne, whose granddaughter, Dorcas, married Sir John Blackwood, and was created Baroness Dufferin and Clandeboye.
The division of the estate was accurately made and decided by lot, which had the effect of putting one branch of the family in possession of the half of the courtyard of the castle which lay nearest the town, while the other part was attached to the castle.
This division caused a family feud of some two hundred years in duration. A house was built on the disputed land between the town and castle, and it was only upon the coming of age of the late Marquis of Dufferin, who said it should never be said of him that he kept any man out of his own hall-door, that the contention ended.
The young nobleman presented the land to his kinsman of the castle, to be held by the tenure of the annual tribute of a red rose to the lady of Clandeboye, or should there be no such person, a pair of gilt spurs to the Lord Dufferin of the time. He added to his gift a castellated gate-house, which was erected from designs by Mr. Ferrers.
The last stone was laid by Lord Dufferin upon the morning of his marriage with Miss Rowan Hamilton on the 23rd of October, 1862.