Majesty
Majesty (His/Her Majesty, oral address Your Majesty) was the correct form of address used for reigning monarchs.
On Earth
On Earth, Majesty was generally used to refer to the monarchs of England and the United Kingdom. Those who were refered to as such included King Richard I, (TV: The Crusade) King John of England, (TV: The King's Demons) Lady Jane Grey, (TV: Lost in Time) King George II, (TV: The Highlanders) Queen Elizabeth I, (TV: The Day of the Doctor, TV: The Chase), King James I, (TV: The Witchfinders) Queen Victoria, (TV: Tooth and Claw, Army of Ghosts) Queen Elizabeth II, (TV: The Idiot's Lantern, The Daleks' Master Plan, Robot, The End of Time, Lost in Time) Elizabeth X, (TV: The Beast Below) an unidentified Queen (TV: Bad Night) and, in an alternate timeline, King John Hart. (AUDIO: The Death of Captain Jack)
Upon being addressed simply as "woman" by Father Angelo, Queen Victoria asserted her form of address before shooting him dead. (TV: Tooth and Claw)
In an alternate timeline, the King John Hart, having been mistakenly addressed as "Your Highness" by Rhys Williams, clarified that was correctly refered to as Majesty while Highness was used for princes. (AUDIO: The Death of Captain Jack)
In France, King Charles IX was refered to as Majesty. (TV: The Massacre)
When trying to gain access to Rosanna Calvierri's school for girls in Venice in 1580, Rory Williams used the psychic paper as a reference from "His Majesty the King of Sweden." (TV: The Vampires of Venice)
On an alternate Earth, Morgaine was addressed as "Your Majesty" by her Knight Commander. (TV: Battlefield)
Elsewhere
In the city of Morphoton on Marinus, Ian Chesterton sarcastically refered to Barbara Wright as "Your Royal Highness" and "Your Majesty" as she was tended to by the city's inhabitants. (TV: The Keys of Marinus)
On Peladon, King Kellian was refered to as "his exalted Majesty". (PROSE: Legacy, TV: The Curse of Peladon) His son, who would become King Peladon of Peladon, (TV: The Curse of Peladon) and granddaughter, the future Queen Thalira, were likewise known as "Majesty". (TV: The Monster of Peladon)
On Draconia, the Draconian Emperor was refered to as Majesty. (TV: Frontier in Space)
On Ravolox, Queen Katryca of the Tribe of the Free was addressed as "Majesty" by Broken Tooth and Sabalom Glitz. (TV: The Mysterious Planet)
Yrcanos, King of the Krontep from Thordon, was addressed as "Your Majesty" by Dorf and the Sixth Doctor. (TV: Mindwarp)
The Viperox Queen was refered to as Majesty by her subordinate, Lord Azlok. (TV: Dreamland)
Emperor Ludens Nimrod Kendrick Cord Longstaff XLI was addressed as "Majesty" by Gloria. (TV: Nightmare in Silver)
According to his wife, River Song, King Hydroflax was properly refered to as "His Infinite Majesty", though he was commonly addressed as simply "Your Majesty". After his disembodied head was destroyed by his metal body, Flemming addressed the King as "your remaining Majesty". (TV: The Husbands of River Song)
