Prince Harry has a book out. It’s called Spare. I’ve not read it and have no intention of discussing either him or the book here.

I’ve nothing against him personally, but I only ever write about the past. As of 2023, the drama of Harry and Meghan still seems to be unfolding very much in the present.

The title of the book interests me though. The monarchy has always felt itself to be strengthened by the existence of 'an heir and a spare'. Currently, Prince William is the heir to the throne and Harry is the spare. Even ignoring the recent problems, it seems very unlikely Harry will ever be king himself. Until 2012, Harry was always third in line to the throne, behind Charles and William. Then, William had three children. Following Charles’ succession last year, Harry is still only fifth in line to the throne, behind William, George, Charlotte and Louis, in that order.

Until 2015, when the rules were changed, the line of succession favoured boys over girls. Under the old ways, Louis would have jumped ahead of his older sister, Charlotte in the line of succession, simply because he was male. This no longer happens.

We expect the monarch of the day to be succeeded by their eldest child. This does, of course, often happen: Elizabeth II succeeded her father in 1952 and Charles succeeded her in 2022.

But it’s surprising how often things go awry. Barely a century has passed since the Norman Conquest of 1066 when the royal line of succession has not been disrupted in some way or another. For example, two of Britain’s three 20th-century kings were second sons. In 1901, Edward VII, the oldest son of Queen Victoria became king as expected. But his own oldest son, Prince Albert Victor had died unexpectedly of pneumonia at the age of 28, nine years before. The young prince had been betrothed to Mary of Teck. Mary now married his younger brother who himself became George V on Edward VII’s death in 1910.

George’s own eldest son, Edward VIII did actually become king, following George’s death in 1936. But he famously abdicated within less than a year. He had no children, so the crown passed to his younger brother, George VI (much to the younger brother’s annoyance).

If history has taught us anything, it’s that this sort of thing happens surprisingly often. For example, for various different reasons, William II, Henry I, Richard the Lionheart, Edward V, Edward VI, Mary Tudor, Elizabeth I, Charles II, Anne, George IV and William IV all died without legitimate heirs. It should be noted, sadly, that Queen Anne had 18 pregnancies, but none of her children survived her. William IV also had ten children but none of them were legitimate and were thus ineligible to become king or queen. It is also interesting to note that after all the struggles Henry VIII had to obtain a legitimate male heir, all three of his legitimate heirs (Edward VI, Mary and Elizabeth) came to the throne and all three died childless.

Other kings such as Richard II, Henry VI, Richard III, Charles I and James II were all overthrown. It is also true that in addition to the examples already given, a number of heirs, for example, Henry VII’s oldest son, Prince Arthur, James I’s heir, Henry and George all died before they were able to become king.

In short, it has always been prudent for a monarch to have an heir and at least one spare whenever possible. The future has always been unpredictable and this can help to consolidate a ruler’s position