All went well until the accession of King
Henry II of England in 1154. Henry invaded Gwynedd in 1157 with the support of
Madog ap Maredudd of Powys and Owain's brother Cadwaladr. The fleet accompanying the invasion made a landing on
Anglesey where it was defeated. Ultimately, at the end of the campaign, Owain was forced to come to terms with Henry, being obliged to surrender Rhuddlan and other conquests in the east. Madog ap Maredudd died in 1160, enabling Owain to regain territory in the east. In 1163 he formed an alliance with
Rhys ap Gruffudd of Deheubarth to challenge English rule. King Henry again invaded Gwynedd in 1165, In the last of his letters to Louis VII of France, he offered to become a vassal of the French king and assist in attacking Henry if the French would make war on him. This time Owain styled himself (Prince of Wales), the first time he or anyone is known to have used such a title. At the time, the word
prince, deriving as it did from the Latin
princeps, meant "first person, chief leader; ruler, sovereign." It wasn't until the 14th century that it came to mean "heir to the throne". Thus, Owain, by designating himself
princeps, was calling himself the principal ruler of Wales. Henry did not invade Gwynedd again, and Owain was able to regain his eastern conquests, recapturing
Rhuddlan Castle in 1167 after a siege of three months. == Disputes with the church and succession ==