Llywelyn Fawr was possibly the most renowned Welsh ruler of the medieval period.
Upon the death of Owain Gwynedd in 1170 AD, his eldest son, Hywel, purportedly a most capable man, succeeded to the rulership of Gwynedd. In Wales, all sons, regardless of their legitimacy, can inherit, provided their father had acknowledged them. This should have been the case with Hywel.
As I wrote in this post, the downside of this enlightened approach to illegitimacy is that it divided the kingdom between all the heirs and fostered animosity among brothers over their portion of their inheritance. Such was the case when Owain Gwynedd overcame his brothers to take the throne, such was the case many years later after the death of Llywelyn Fawr, and such was the case in 1170.
Thus, Dafydd ap Owain Gywnedd conspired with his mother (Owain Gwynedd’s second wife, Cristina) and brother Rhodri to usurp the throne from Hywel, the eddling, whom his father had chosen to succeed him. Dafydd drove Hywel out of Gwynedd and ultimately defeated him at the battle of Pentraeth. After the untimely and suspicious deaths of most of Dafydd’s other brothers, Dafydd eventually ruled most of Gwynedd and parts of Wales all by himself from 1174. http://en.academic.ru/dic.nsf/enwiki/1255610
Llywelyn ap Iorwerth was born in 1172, at the remote castle of Dolwyddelan, south of Mt. Snowdon.
Iorwerth, Llywelyn’s father, was the eldest legitimate son of Owain Gwynedd, by his first wife Gwladys. He married Marared, daughter of Madog ap Maredudd, Prince of Powys. Thus, Llywelyn was grandson to Owain Gwynedd and of a powerful lineage on both sides.
“The infant prince, being a potential menace to the power of his father’s half-brothers in Gwynedd , probably grew up in Powys under the protection of his maternal relatives. Following an obscure period of apprenticeship in arms (he entered the turbulent arena of northern politics at a very tender age), he combined with his cousins, the sons of Cynan ap Owain Gwynedd, and in 1194 defeated his uncle, Dafydd I, seizing from him a share in the government of Perfeddwlad, which in 1197, he transformed into sole rulership. With the capture of Mold in 1199 he promised to become a leader of the calibre and vision of Owain Gwynedd; in fact, between 1199 and 1203 , he restored the undivided sovereignty of his grandfather over the whole of Gwynedd , including Merioneth and Penllyn .” In 1194, he was only 22.