He was a son of Cyngen ap Cadell the last King of Powys of the Gwertherion (Vortigern) Dynasty who claimed descent through Brochwel Ysgithrog.
His sister Nest ferch Cadell then married Merfyn (Frych) Ap Gwriadone (or possibly Mefyn's father Gwriad ab Elidir, depending on which genealogy one gives authority to) and they became the parents of Rhodri Mawr, ruler of Gwynedd, who then unified Wales under his rule.
Lewys Dwnn in his visitation to Wales reports "Cadell ap Brochwell had but one daughter named Nest, who carried off the Province from the males, as appeareth, etc" (vol.
It may be that Gruffydd was the eldest son, and through this murder Elisedd claimed his lands and titles - but this is only conjecture.
When the herald Lewys Dwnn visited Wales between 1586 and 1613 to gather pedigrees that would clarify the inherited status and titles of the leading families of Powys, many of them claimed princely blood by descent from children of Cyngen.