When Wallis Simpson (or rather Mrs Wallis Warfield as she was known at the time) married His Royal Highness The Duke of Windsor on 3 June 1937, she should have become Her Royal Highness The Duchess of Windsor. But, she was denied the style of HRH with her husband bitterly commenting that it was a “nice wedding present.”
This decision was against the royal practice, and British common law as a wife automatically takes her status from her husband unless her own rank is higher. When Lady Elizabeth Bowes-Lyon married the Duke of York (future King George VI), this statement was released: “In accordance with the settled general rule that a wife takes the status of her husband Lady Elizabeth Bowes-Lyon on her marriage has become Her Royal Highness the Duchess of York with the status of a Princess.”1 The Duke of Windsor had been assured by his brother that Wallis would become part of the family upon marriage and as it had been agreed to treat the Duke of Windsor as a junior Royal Duke, his wife would have ranked in precedence just behind her two sisters-in-law, the Duchesses of Kent and Gloucester.
In a letter from King George VI to his brother, he explained that he had consulted the heads of the Dominion and Empire countries and that they had advised that they considered that he had lost all royal rank when he abdicated the throne and was no longer entitled to use the title of Prince or the style of HRH. On 26 May 1937, the discussion and ratification of the Letters Patent that created the former King a Royal Prince and allowing him to withhold the style of HRH from Wallis were included in Stanley Baldwin’s last Cabinet meeting as Prime Minister. Two days later, the official announcement appeared in the London Gazette.2 The former King had, according to them, lost all royal rank upon abdication, and the new King was perfectly entitled to restore this rank and to restrict the style of HRH to him alone. (Read more about denying the style of Royal Highness to Wallis here)
However, the former King never lost his royal rank. On 5 February 1864, Queen Victoria had issued Letters Patent saying, “that besides the Children of Sovereigns of these Realms, the Children of the Sons of any Sovereign of Great Britain and Ireland shall have and at all times hold and enjoy the title, style and attribute of “Royal Highness,” with their titular dignity of Prince or Princess prefixed to their representative Christian names.”3 Queen Victoria’s Letters Patent were later confirmed by King George V in 1917.4 Upon his abdication, he immediately became a Prince of the United Kingdom of Great Britain and Ireland with the qualification of Royal Highness pursuant to the 1917 Letters Patent, confirmed by his own father. King George VI had even – inadvertently – recognised his brother’s royal rank immediately after his abdication by instructing Sir John Reith to introduce him as His Royal Highness Prince Edward before his speech to the nation.
Thus, even if you consider the denying of the style of HRH to the Duchess of Windsor to be valid, she still married a royal Prince and held the status of a Princess.
For almost 50 years, the United Kingdom had a royal Duchess with the status of a Princess whom they stubbornly (if at all) addressed as “Her Grace.”