Image: Princess Elizabeth, as she was then, and Princess Margaret at a rehearsal for their father's coronation in 1937.

Since George V issued Letters Patent in December 1917, the rules, in the UK at least, as to who can be called Prince or Princess have been very clear. With an eye on an ever-expanding family and his German relatives, where the world and his wife were allowed the honour, King George decided instead to restrict the style and the use of HRH to immediate members of the Royal Family only.

The Letters Patent specifically states:

"…that the children of any Sovereign of the United Kingdom and the children of the sons of any such Sovereign and the eldest living son of the eldest son of The Prince of Wales shall have and at all times hold and enjoy the style, title or attribute of Royal Highness with their titular dignity of Prince or Princess prefixed to their respective Christian name…"

With this ruling his great-grandchildren, and the children of his daughter, would no longer be allowed to use HRH nor would they be styled Prince or Princess. This was the first time a Letters Patent actively restricted the usage of royal titles in the male line. George V did not, at this time, have grandchildren.

A few months before this ruling, on 17 July 1917, George V had also changed the name of the Royal Family from the House of Saxe-Coburg and Gotha, to the House of Windsor. During the First World War, many felt uncomfortable with the Royal Family’s connection to Germany. The King’s change of the Royal family name, the relinquishment of German titles and styles, and the restriction of who could and could not be HRH and Prince/Princess was one way of distancing the Family from the aggressor. In compensation, British peerages were awarded to various cousins who complied with this order, such as Louis of Battenburg, who became Louis Mountbatten, 1st Marquess of Milford Haven.

There are two ways one can become a Princess in the UK: by marriage or by birth. The only way to become a Prince in this country is to be born one. Archie, the only son of The Duke and Duchess of Sussex, was not styled a Prince at birth, as he was then a great-grandson of the monarch. Since the late Queen’s death in September, however, and with his grandfather’s accession to the throne, he now falls under the 1917 ruling and can be styled Prince Archie of Sussex, if he so chooses.

When Catherine Middleton married Prince William in 2011, she did not become Princess Catherine – she became Princess William of Cambridge, or more commonly, the Duchess of Cambridge. The Queen awarding the dukedom to Prince William on the occasion of his marriage meant Catherine was not referred to as Princess William until her husband became The Prince of Wales.

Similarly, when Meghan Markle married Prince Harry in 2018, she did not take on the style of Princess Henry because of the Queen’s gift of the dukedom of Sussex to her grandson. And Sophie did not take the style of Princess Edward because of the Earldom of Wessex.

However, this does not apply to daughters born into the Royal Family. When Charlotte was born in 2015 she was automatically styled Princess Charlotte because the late Queen had already issued Letters Patent extending the scope of the 1917 ruling to all the Cambridge children:

"The Queen has been pleased by Letters Patent under the Great Seal of the Realm dated 31 December 2012 to declare that all the children of the eldest son of The Prince of Wales should have and enjoy the style, title and attribute of Royal Highness with the titular dignity of Prince or Princess prefixed to their Christian names or with such other titles of honour."

The Sussex children were not, while the late Queen was alive, entitled to use the style of Prince or Princess but once their grandfather became King, they as grandchildren of the monarch, were automatically afforded the style of HRH and Prince/Princess. They do not have to use these styles, and given that their parents no longer use HRH, it is likely that they will follow suit.

There are other examples of non-use of the style of Prince/Princess within the current Royal Family. The Wessex children, as children of the son of a monarch could have been style Prince James and Princess Louise. Instead, in consultation with the late Queen, their parents decided they should use the styles of children of a peer. In other words, James would use his father’s secondary title, Viscount Severn, and Louise, would be styled Lady Louise:

The Queen has also decided, with the agreement of The Prince Edward and Miss Rhys-Jones, that any children they might have should not be given the style His or Her Royal Highness, but would have courtesy titles as sons or daughters of an Earl.
Press Release - Saturday 19th June, 1999

Currently, in the UK, only 24 people would use the title Prince or Princess. It is an exclusive club, surely what George V wanted when he signed the Letters Patent back in 1917.

The Prince of Wales

The Princess of Wales (Princess William of Wales)

Prince George of Wales

Princess Charlotte of Wales

Prince Louis of Wales

The Duke of Sussex (Prince Henry of Sussex)

The Duchess of Sussex (Princess Henry of Sussex)

Prince Archie of Sussex

Princess Lilibet of Sussex

The Duke of York

Princess Beatrice of York

Princess Eugenie of York

The Princess Royal

The Earl of Wessex (Prince Edward of Wessex)

The Countess of Wessex (Princess Edward of Wessex)

Viscount Severn

Lady Louise Mountbatten-Windsor

Duke of Kent

Duchess of Kent

Prince Michael of Kent

Princess Michael of Kent

Princess Alexandra

Duke of Gloucester

Duchess of Gloucester

Note: When Sarah Ferguson married Prince Andrew in 1986, she became a princess by marriage. Since her divorce in 1996, however, she lost the right to use HRH and has been known as The Duchess of York and should not be referred to by any other style.