According to "Koshi kafu," Hiromoto was a son of FUJIWARA no Mitsuyoshi, and he was said to have been brought up under NAKAHARA no Hirosue who was a remarried husband of his mother.
広元は『江氏家譜』では藤原光能の息子で、母の再婚相手である中原広季のもとで養育されたと言われる。