In 1708, he became a yushi (another child considered as one's own) of Emperor Higashiyama and received the Emperor's proclamation for being an Imperial Prince in June and July 1709 and was named Sadatake.
宝永5年（1708年）東山天皇の猶子となり、翌宝永6年（1715年）5月親王宣下を蒙り、貞建と命名される。