Although he once left the Imperial Family and was granted the surname of Genji and called MINAMOTO no Sadami, he returned to the Imperial Family on August 29, 887 with the help of Kampaku, chief adviser to the Emperor, FUJIWARA no Mototsune, and became a prince on August 30, 888.
一度臣籍降下し、源氏の姓を賜って源定省を称したが、後に実力者の関白藤原基経の後押しで887年（仁和3年）8月25日に皇族に復帰し、翌8月26日に皇太子に立てられる。