He was adopted by Emperor Shirakawa and was first regarded as successor of the emperor, but he went through shinsekikoka (leaving the imperial family and becoming a subject of the emperor) in 1119, having a family name of Minamoto from the emperor because Emperor Toba, a grandson of Emperor Shirakawa had a baby which was named Imperial Prince Akihito (later, Emperor Sutoku).
始め白河天皇の養子となり皇嗣と目されたが、院の孫鳥羽天皇に顕仁親王（後の崇徳天皇）が生まれたことから元永2年（1119年）源姓を賜り臣籍降下。