At present, the Imperial House Act determines that the title of honor for it is 'her Majesty' but, in old days, it was honorably referred to by adding a letter 'Miya (imperial princess, etc)' as in Kotaigo-Miya.
皇室典範により現在の敬称は「陛下」と定められるが、古くは皇太后宮という様に「宮」（ぐう）の字をつけて敬称した。