c.1605 William Shakespeare, Macbeth, Act 1, scene 6:
All our service,
In every point twice done and then double done,
Were poor and single business to contend
Against whose honors deep and broad wherewith
Your Majesty loads our house.
c.1845 Alexandre Dumas, The Count of Monte-Cristo, page 59:
“ Sire,” said Villefort, “ the rapidity of the event must prove to your majesty that God alone can prevent it, by raising a tempest ; what your majesty is pleased to attribute to me as profound perspicacity is simply owing to chance ; and I have profited by that chance, like a good and devoted servant—that's all. Do not attribute to me more than I deserve, sire, that your majesty may never have occasion to recall the first opinion you have been pleased to form of me.”
This is the second-person form of address. Verbs used with this pronoun as the subject are conjugated in the third person. The forms used in the third person are His Majesty (for a king or emperor) and Her Majesty (for a queen or empress).
If the reigning monarch is a prince or princess, the form is Your Highness.
The exact forms vary somewhat from country to country.