After Meghan Markle marries Prince Harry, she will not become a Princess Meghan. Let’s sort this out.
There is a simple and cruel answer: she has no Royal blood.
Once the actress marries the Prince, she will be automatically called HRH, Princess Harry of Wales.
Kate Middleton with Prince William had equal situation, where she was called HRH, Princess William of Wales. There’s the same cause — Kate had no royal blood. Identical rules should be applied to Meghan.
“Prince” or “Princess” titles can be given due to own royal origin, and marriage plays no role in Britain.
Due to these rules, we may also say that there had never been Princess Diana. Diana Spenser became the Princess of Wales, and once there was a divorce with Prince Charles - Diana, the Princess of Wales. In English tradition these are two different titles in the hierarchy of aristocracy in Britain.
Also Sarah Ferguson had no title of Princess Sarah. Prince Edward’s spouse — Sophie Rhys-Jones cannot be entitled as Princess Sophie.
One journalist told, that the Royal Family could not flourish for about a thousand years having no solutions of such problem about how to call each other.
After Prince Andrew took Sarah Ferguson to wife in 1896, the Queen entitled him as a Duke of York, and Ferguson respectively - the Duchess of York. Ferguson kept this title even after marital disruption.
Prince Edward with Sophie Rhys-Jones had similar situation - he was entitled as the Earl of Wessex. Sophie respectively - the Countess of Wessex.
Probably equal situation can happen to Prince Harry and Meghan by entitling the grandson a Duke of Sussex, Olbany or Clarence.
Queen (or future King) in theory can make Kate and Meghan princesses. But due
to strict traditions, we could hardly hear the name of Princess Meghan in the nearest
Based on materials bbc.com