That’s because when Edward and Sophie married in 1999, Buckingham Palace announced they were given the title of the Earl and Countess of Wessex and their children “would have courtesy titles as sons or daughters of an earl”.
Courtesy titles are only used by the peer’s eldest living son, and the eldest son’s eldest living son, and so forth. Other descendants, like Louise, are not permitted to use the peer’s subsidiary titles. Only the heir apparent (and heir apparent to the heir apparent, and so on) may use them.
Since Louise is the daughter of an earl, was was given the lady title after her birth in 2003.
Similarly, Charles Spencer’s daughters are simply known as Lady Kitty, Lady Amelia, Lady Eliza, Lady Lara and Lady Charlotte, while his fourth-born child – but his eldest son – is known as Louis Spencer, Viscount Althorp.
But, whilst the Earl of Wessex is a hereditary title, Edward’s Duke of Edinburgh title is not.
That means that after his passing, the Duke of Edinburgh title will go back to the Crown, with Prince William and Princess Kate’s children, especially Prince Louis, being the top candidates.
