The dignity and authority of sovereign power; quality or state which inspires awe or reverence; grandeur; exalted dignity, whether proceeding from rank, character, or bearing; imposing loftiness; stateliness; usually applied to the rank and dignity of sovereigns
politeness You use majesty in expressions such as Your Majesty or Her Majesty when you are addressing or referring to a King or Queen. His Majesty requests your presence in the royal chambers
Hence, used with the possessive pronoun, the title of an emperor, king or queen; in this sense taking a plural; as, their majesties attended the concert