Martha

Martha, or Her Royal Highness Princess Philip of Wales is the wife of Prince Phillip of Wales.

Title and Style
Though known as "Martha" in Red White and Royal Blue, her rank as a Princess (by marriage) of the United Kingdom entitles her to the style of Her Royal Highness. Her formal title depends on whether Prince Philip also holds a peerage (such as a royal dukedom typically conferred on senior princes of the blood upon marriage). If, for example, Philip were created Duke of Kent, Martha would correctly be styled Her Royal Highness The Duchess of Kent. If he does not hold a peerage, Martha's formal style would be Her Royal Highness Princess Philip of Wales. She would be referred to as Princess Martha only colloquially (and technically incorrectly), or by special permission granted by the sovereign (for example, after the death of the husband from whom she drew her name).