The King etc
The monarch is His or Her Majesty (HM). Princes and princesses are His or Her Royal Highness (HRH) though this courtesy title may be withdrawn, as in the case of Princess Diana after her divorce, or withheld, as in the case of the Duchess of Windsor. As usual with capitals, a particular person takes a cap, such as the Queen or Prince George. If you are referring to princes or queens in general, they are lower case.
Since the death of Queen Elizabeth II on September 8, 2022, this is the line of succession to the throne.
1. HRH Prince William, Prince of Wales (King Charles III's elder son) (he may be called the heir to the throne or the heir apparent, but not heir apparent to the throne)
2. HRH Prince George of Wales (elder son of the Prince and Princess of Wales)
3. HRH Princess Charlotte of Wales (daughter of the Prince and Princess of Wales)
4. HRH Prince Louis of Wales (younger son of the Prince and Princess of Wales)
5. HRH Prince Henry, always known as Prince Harry, Duke of Sussex (King Charles’s younger son)
6. Archie Harrison Mountbatten-Windsor, son of the Duke and Duchess of Sussex (formerly Meghan Markle). As the grandson of the monarch he is legally a prince and entitled to be called HRH but at time of writing his parents have not confirmed if he will use the title.
7. Lilibet Diana Mountbatten-Windsor, daughter of the Duke and Duchess of Sussex. See the above note about Archie - the same applies to Lilibet.
8. Prince Andrew, Duke of York (Prince Charles’s younger brother, the Queen’s second son). He has the title HRH but does not use it in any official capacity.
9. HRH Princess Beatrice of York (Prince Andrew’s elder daughter), Mrs Edoardo Mapelli Mozzi
10. Miss Sienna Mapelli Mozzi, daughter of Princess Beatrice
11. HRH Princess Eugenie of York (Prince Andrew’s younger daughter), Mrs Jack Brooksbank
12. Master August Brooksbank, Princess Eugenie's son
13. HRH Prince Edward, Earl of Wessex (King Charles’s youngest brother, Queen Elizabeth’s third son)
14. James, Viscount Severn (Prince Edward’s son)
15. Lady Louise Mountbatten-Windsor (Prince Edward’s daughter)
16. HRH Princess Anne, Princess Royal (King Charles’s sister, Queen Elizabeth’s second child and only daughter).
You can find the complete list as far as 100 on this website: https://britroyals.com/succession.asp
the King reigns, he does not rule.
Individuals are ‘presented’ to the King. He is not introduced or presented to them.
In headlines about the King or royalty, please don’t use ‘one’ on every single story. It might have been smart the first few hundred times, but now it is lazy and boring. When the Queen was alive there were also many dreadful headings involving ‘Ma’am’ and ‘we are/she is not amused’. (Mail Online hit the jackpot in September 2015 with ‘One is amused’.) It remains to be seen what cliches will take hold about King Charles, but one has already made an appearance on stories about Prince George - the very witty ‘By George!’ Spare us.
If members of the Royal Family (note: caps only for the British Royal Family, not foreign ones) have extra titles conferred on them by the late Queen or in future by the King, these are the more senior titles and in theory should be used on first reference. For example Prince William was given the title Prince of Wales on the accession of his father, the previous Prince of Wales, to the throne. From now on he should be called the Prince of Wales first, then Prince William. In headings and captions, William (or at a pinch Wills, though this is a bit familiar for my taste) is fine.
Similarly, Princess Anne should be the Princess Royal at first mention and then the Princess or Anne. Diana, Princess of Wales, should not be called ‘Princess Diana’ but I doubt if anyone will ever take any notice (this form of address was announced by Buckingham Palace after her divorce). The Princess of Wales should have her full title at the first reference, but can be Kate, Catherine or the Princess thereafter. Kate is fine for captions and headings. Occasionally she is still referred to as Kate Middleton, but since the couple married in 2011 this strikes me as odd.
Princess Michael of Kent: Traditionally wives of royalty take their husband’s title and name if they do not have a senior title of their own. Prince Michael of Kent does not hold a dukedom so his wife Marie-Christine is Princess Michael. It does not work the other way round, so when a man marries a princess, it does not make him a prince.
Lady: This is the cause of a lot of anguish but the rule is fairly simple. The daughter of a duke, marquess or earl is called Lady Firstname Surname from birth, eg Lady Lara King. When she marries, either someone with a title or without, she retains Lady Lara and takes her husband’s surname (if he is a commoner, he remains Mr). No other rank of woman is Lady Firstname Surname.
When Lady Antonia Pakenham, the daughter of the Earl of Longford, married Sir Hugh Fraser, she became Lady Antonia Fraser, or Lady Antonia in the second reference. When she married Mr Harold Pinter she became Lady Antonia Pinter.
A woman without her own title by birth who marries a man who has the title Sir or Lord becomes Lady Surname (no first name). So, if Miss Elizabeth Ashworth marries Sir Mick Jagger, she becomes Lady Jagger. If you want to put in her first name, you can do it by saying ‘Sir Mick Jagger and his wife Elizabeth’, or ‘Sir Mick and his wife, the former Elizabeth Ashworth’, but you never call her ‘Lady Elizabeth Jagger’ or ‘Lady Elizabeth’.
The younger sons of earls, and the sons and daughters of a viscount or baron, have the title ‘the Honourable’, usually shortened to ‘the Hon’. The daughter of a viscount or baron who marries a commoner is the Hon Mrs Smith.
The divorced wife of a peer conventionally keeps the title but puts her first name in front of it to distinguish her from any subsequent wives. So the Duchess of York should now be Sarah, Duchess of York, even though we will probably never call her anything but Fergie.
A dowager is the widow of a peer. The term is used particularly if a married son has inherited the title, to avoid having two women with identical styles. So you would have the Dowager Countess of Bromley and her daughter-in-law, the Countess of Bromley. A queen dowager is the widow of a king.
A baronet is a hereditary title but is not a peerage, so the holder is a commoner. In other words he should not be called a member of the nobility or aristocracy. A baronet is styled ‘Sir’ like a knight, but can have the abbreviation Bt after the name, eg ‘Sir Stanley Smith Bt’.
life peers are not aristocracy (except in the rare case when a title-holder by birth is awarded an additional life peerage). See the Politics section for more.
There is a multitude of other rules about royal and aristocratic titles, but you will very rarely need to know them. If you do, I suggest you consult the Daily Telegraph stylebook online.
Abdication: Cap with specific reference to Edward VIII; in general sense, use l/c.
curtsey, not curtsy: Therefore present tense is curtseys, not curtsies, past tense is curtseyed, not curtsied.
Marquess: This is a man, eg the Marquess of Bath (Marquis is a foreign title). A woman with the rank of a marquess, or the wife of a marquess, is a Marchioness.
Royal Wedding: I can’t think of a logical reason for caps on this but this is how it appears most of the time.
royals: Use only as a last resort, and l/c.