During the French RevolutionLouis XVI had to change his title to indicate he was "king of the French" rather than "king of France", paralleling the title of "king of the Franks" (rex Francorum) used in medieval France.
Currently, Belgium has the only explicit popular monarchy, the formal title of its king being King of the Belgians rather than King of Belgium. Constitutional monarchy in the modern sense can be considered an evolution of the idea, as such constitutions generally place sovereignty with the people, not the monarch.
The first Portuguese king, Afonso Henriques, used the style King of the Portuguese (Rex Portugalensium), to remember that he was elected on the battlefield, after the Battle of Ourique (1139), by his fellows and subjects; their descendants, instead, used the style of King of Portugal (Rex Portugaliae or later in Portuguese: Rei de Portugal).
Used by Zog I, the one ruler of the Kingdom of Albania, from 1928 de facto to 1939, and de jure until 1946. Victor Emmanuel III, who claimed the Albanian throne between 1939 and 1943, used the title King of Albania.
Rex Anglorum Saxonum or Rex Anglorum in Medieval Latin. Used by the Anglo-Saxon kings of England. The title King of the Anglo-Saxons was first adopted by Alfred the Great when the people of Mercia accepted him as their ruler in the late 9th century. The first king to style himself King of the English was Æthelstan when he conquered the Norse Kingdom of York in 927, making him the first ruler of a united England.
This usage became less common with William and Mary, who chose to be called King and Queen of Scotland. The Acts of Union 1707 abolished the Scottish and English thrones and created the Kingdom of Great Britain.
Evolving from King of the Britons, before mediatising in the 12th century as Prince of the Welsh. Eventually, Dafydd II of Gwynedd and Wales adopted the title Prince of Wales to denote suzerainty over the whole of Wales, not just the Welsh people.
The official title of Ferdinand I in 1908–1918, Ferdinand's son Boris III (1918–1943) and Boris' son Simeon II (1943 – at least to 1946) was: by the Grace of God and the People's Will King of the Bulgarians. In fact, Ferdinand I was elected by the National Assembly as a Prince of Bulgaria in 1887.