Prince Atsuyasu was born in 999 to Emperor Ichijo (the 66th Emperor) and FUJIWARA no Teishi, who was the then Chugu (the second consort of an emperor), at the residence of TAIRA no Narimasa, who served as Chugu no Daishin (a sixth rank post in the Office of the Empress's Household).
第66代一条天皇を父に、中宮藤原定子を母として、長保元年（999年）中宮大進平生昌邸において誕生。