Cadwaladr ap Gruffydd was Owain Gwynedd’s brother. In a startling, and yet unsurprising, parallel to the relationship between Llywelyn ap Gruffydd (d. 1282) and his younger brother, Dafydd, Cadwaladr and Owain were often at odds. As was the case with Llywelyn, Owain was a second son. He (unlike Llywelyn, who kept his elder brother in prison) became the eldest son when his brother, Cadwallon, died, leaving Owain and Cadwaladr to rule without him. In Wales, unlike in England, all sons inherit lands when their father dies. This caused problems for Wales time and again–as the brothers fought over lands among themselves and what had been a united kingdom under the father became divided under the sons.
In the case of Llywelyn and Dafydd, Llywelyn (at 13 years older) had long-established his rule of Gwynedd before his brother came of age, and was reluctant to ‘share’ his inheritance with his younger brothers. Owain and Cadwaladr, on the other hand, seemed to have split their territory amicably at first, but in 1143 AD, “Cadwaladr’s men killed Anarawd ap Gruffydd of Deheubarth by treachery, apparently on Cadwaladr’s orders.” Owain Gwynedd had intended Anarawd to become his son in law and “responded by sending his son Hywel ab Owain Gwynedd to deprive Cadwaladr of his lands in Ceredigion. Cadwaladr fled to Ireland where he hired a fleet from the Danish settlement in Dublin and landed at Abermenai in 1144 in an attempt to force Owain to return his lands. Cadwaladr apparently abandoned or escaped from his allies and made peace with his brother, who obliged the Danes to leave.”
Things remained uneasy between the brothers for the rest of their lives. In 1147, the brothers fought again, resulting in Cadwaladr’s loss of Meirionydd. Their animosity was further exacerbated by the fact that Cadwaladr sided with King Henry II in 1157 AD when he invaded Wales. Cadwaladr, through his marriage to Alice Fitz Gilbert, had become a land owner in Lancashire and Shropshire.
That war resulted in a stalemate, with Owain giving homage to Henry and Cadwaladr receiving some of his lands back, but with no real gains by Henry into Owain’s territory.
In the end, Cadwaladr outlived Owain but didn’t again attempt to share power with him.