The Lord of Black Castle by Kathryn Le Veque

The ultimate enemies to lovers trope has arrived as a brutal Irish knight conquers his hatred of the English to win the heart of the sister of his English enemy.

Welcome to the wilds of Medieval Ireland…

1323 A.D. – Devlin de Bermingham, an Irish knight to the core, is the bastard son of the Earl of Louth and the descendant of Irish kings. He is also a strong proponent that the Irish should rule Irish lands. Rebelling against his English overlord, the Earl of Kildare, he captures one of Kildare’s castles south of Wicklow.
Known as Black Sword, a rebel who is both admired and feared, Devlin has set the events in motion for an enormous Irish revolt. Every Norman settlement in Ireland is at risk because of Black Sword’s actions and the stage is set.

The Lady Emllyn Fitzgerald is the sister of the Earl of Kildare. When her brother sends his fleet to quell the uprising on his lands, she stows away on one of the vessels in order to follow the object of her affection, a strong young English knight sworn to her brother, into battle. It is her intention to prove to the man she is worthy and brave enough to be his wife, but she truly has no grasp of the seriousness of her folly.