He was first called (Prince) Sukesada, and after he had lost his father Imperial Prince Tomohira early, became a Yushi (another child considered as one's own) of FUJIWARA no Yorimichi, who was the husband of his elder sister Princess Takahime (however, at that time, Yushi were considered to be virtually same as an adopted child.)
はじめ資定(王)（すけさだ(おう)）と称し、父具平親王を早くに亡くし、姉・隆姫女王の夫である藤原頼通の猶子となった（ただし、当時の実態とすれば養子とほぼ同様の意味に解する事ができる）。