This was due to the fact that the father of the princess of Imperial Prince Tamehira was Sadaijin MINAMOTO no Takaakira, and the Fujiwara clan feared that if Imperial Prince Tamehira became Crown Prince and assumed the Imperial Throne, MINAMOTO no Takaakira would become a maternal relative and could be placed in a dominant position.
これは為平親王の妃の父が左大臣源高明であり、もしも、為平親王が東宮となり将来皇位につくことになれば源高明が外戚となり権勢を振るうことになりかねず、これを藤原氏が恐れたためであった。