Since there is mention of 'the third one not being of respectable character' within the section of the "Eiga Monogatari" (Tale of Glory) that introduces Tadahira's children, it is presumed that Moroyasu was Tadahira's third son.
『栄花物語』の忠平の子息を紹介する段に「三郎の御有様おぼつかなし」とあるので、師保は忠平の三男であると推測される。