藤姓とは、朝業の実家である宇都宮氏が藤原氏の出自であったためである。

The name FUJIWARA came from the UTSUNOMIYA clan, which was Tomonari's family home and had originated with the FUJIWARA clan. - Wikipedia日英京都関連文書対訳コーパス

藤原実家（ふじわらのさねいえ、久安元年（1145年）-建久4年3月16日（1193年4月19日））は、平安時代後期の公卿・歌人。

FUJIWARA no Saneie (1145 – April 26, 1193) was a court noble and poet of the late Heian period. - Wikipedia日英京都関連文書対訳コーパス

しかし、当時外祖父・中関白藤原道隆は既になく、また伯父藤原伊周の失脚で母の実家は没落し力を失っていた。

However, because of the death of FUJIWARA no Michitaka (also known as Nakanokanpaku), his maternal grandfather, as well as the downfall of FUJIWARA no Korechika, his uncle, the family into which his mother was born had already fallen into ruin and lost influence before he was born. - Wikipedia日英京都関連文書対訳コーパス