UPD: Таки да, не знаю:
"‘His, Her, Your, (etc.) Highness’ was formerly the title of English kings and queens, varying with ‘Grace’, and later with ‘Majesty’. In the Dedication of the Bible of 1611 to James 1, ‘Highness’ and ‘Majesty’ are used indifferently, as they had been in reference to Queen Elizabeth; but in his reign ‘Majesty’ became the official style." (OED, статья Highness). Отдельное спасибо Кате Доброхотовой за коммент на фейсбуке!