Quote Originally Posted by Chas View Post
Just like William's mother was incorrectly called "Princess Diana or Di".

As an alternative she could be called Her Royal Highness Catherine, The Duchess of Cambridge. A shorter and slightly less formal style.

Chas
My understanding is that she would be called Her Royal Highness, The Duchess of Cambridge. If she were HRH Catherine, The Duchess of Cambridge, she would be the widowed mother of the present Duke of Cambridge - which clearly the former Catherine Middleton is not.