The title of Princess Royal is usually granted by the British monarch to their eldest daughter. It was Henrietta Maria of France, consort of King Charles I, who wanted to have a title similar to the “Madame Royale” title in France. It was their daughter Mary who became the first Princess Royal in 1642. However, the French Madame Royale was often used for the eldest unmarried daughter and could pass to the next daughter when the elder married. The British Princess Royal title is for life and can only be granted again when the holder dies.
So far, there have been seven Princesses Royal.
The Princess Royal: From Princess Mary to Princess Annel by Helen Cathcart covers all seven of these women, but most of the book is spent on the latest Princess Royal, Anne. The information seems to be factual, and the book is easy to read. However, the original version of this book is from the 80s, and although it has been given a new cover, the information has not been updated. I would consider this an enormous miss. I can’t even imagine publishing a book again and not updating it, even though so much time has passed.
Don’t even bother.