The use of the title of Princess of the United Kingdom of Great Britain and Northern Ireland is entirely at the will of the sovereign, and is now expressed in letters patent. Individuals holding the title of princess are styled "Her Royal Highness" (HRH). The current letters patent were issued in 1917 during the First World War, with one extension in 2012.
Anne, Princess Royal, daughter of Elizabeth II, granddaughter of George VI and princess of the blood
Frederica of Hanover was Queen of Greece from 1 April 1947 until 6 March 1964 as the wife of King Paul.
Frederica before her arrival in Greece
Queen Frederica with King Paul, while visiting the USS Providence (CL-82), at Athens, circa May 1947
On the cover of Time, 1953
"COMING!!! The people's 'beloved' queen mother Frederica". Anti-monarchy poster of Queen Frederika from the 1974 referendum.