btw kate is not a princess, nor was diana a princess
Well, they are/were princesses by marriage and are entitled to use the title.
In all, there are currently ten people entitled to use the title “Princess” in the UK:
The Duchess of Cornwall (who holds legal title to the style “Princess of Wales” even if she does not use it).
The Duchess of Cambridge
Princess Beatrice of York
Princess Eugenie of York
Lady Louise Windsor (who is legally entitled to use the style of “Princess Louise of Wessex” but does not do so at her parents wishes).
Princess Anne
The Duchess of Gloucester
The Duchess of Kent
Princess Michael of Kent
Princess Alexandra
Of these, only Beatrice, Eugenie, Louise, Anne and Alexandra are princesses by birth and hence known as Princess (first name).
The Wolf