[strandinthewind]

Also - from the same source:

The style "Princess Diana" was always incorrect, though often used by the public and the media. With rare exceptions, as in the case of Princess Alice, Duchess of Gloucester, only women born to the title (such as Princess Anne) may use it before their given names. After her divorce in 1996, Diana was officially titled "Diana, Princess of Wales", based on a provision in the divorce settlement signed by the Queen, although she could not be called "Her Royal Highness." Even the style "Princess of Wales" would have lapsed had Diana remarried. Had she lived, Diana might have had her royal status restored to her by her son, Prince William, upon his accession to the throne.

During her marriage to Charles, her full title was Her Royal Highness The Princess Charles, Princess of Wales, Duchess of Cornwall and Countess of Chester, Duchess of Rothesay, Countess of Carrick, Baroness of Renfrew, Lady of the Isles, Princess and Great Stewardess of Scotland