Some of the genealogies give Bleddyn as the eldest son, which does not seem to be in accord with the recovery of the lordship of Whittington, and other facts. We therefore prefer to regard Goronwy, and perhaps other children who died young, as senior to Bleddyn.
Bleddyn was the second son of Tudur ap Rhys Sais. Very little is known regarding him. He is described as of Pengwern.

Sir John Rhys, speaking of Bleddyn ap Tudur's day, says: "the kingdom or principality of Powys was now practically at an end, and the surviving members of the Welsh princely cenedloedd of that region had become vassals of the king [of England]. The whole of Cymru [Wales] except Gwynedd was divided between Norman and Welsh lords, who came to be called Lords-Marchers. . . .
"In the south and in Powys the possession of the descendants of the princely houses dwindled down to cymwyds or cantrefs, largely those of the more mountainous parts of the country, held more or less voluntarily as vassals of the Norman king; but in these sadly diminshed areas the cyfraith gyffredin (common law) of Cymru was still the rule of right. The chieftains, though reduced in power, kept up according to their means the household state found in Howel's laws, haughtily cherished the memories of a departed greatness, and alternately sullenly acquiesced in the new state of things and eagerly seized an opportunity for revenge against Norman, Saxon, and Cymric neighbor alike."
Maredydd, the son of Bleddyn Prince of Powys, notwithstanding the difficulties which presented themselves, succeeded, before his death in 1129, in regaining quite a considerable portion of the kingdom over which his father had reigned, including the lordship of Nanheudwy, and other lands which had formerly belonged to the Norman earldom of Shrewsbury. At his death, Maredydd divided his territory between his son Madog, and his grandson, Owain. Madog received Northern Powys, including Nanheudwy and Maelor Saesneg, from which it acquired the name of Powys Fadog. Owain was was given "Upper Powys," afterwards known as Powys Wenwynwyn. Thus Bleddyn ap Tudur of Pengwern and his descendants came to hold their lands under the princes, or lords of Powys Fadog, until the fatal year of 1282.
Bleddyn is stated to have married Annesta, daughter of Llywelyn ap Idnerth ap Maredydd Hên (the elder) of Buallt, in Powysland; by whom, according to several pedigrees, he had issue: Owain, Madog, and Bleddyn Fychan. Dwnn, however, gives the children of Bleddyn as Owain, ancestor to the Mostyn family, Iorwerth, Cynfrig, and Heilin.
The Welsh People, Rhys and Brynmor-Jones, 4th ed., pp. 300-304.