Monsieur

Monsieur (French pronunciation: ​[møˈsjø]; pl. Messieurs; 1512, from Middle French mon sieur, literally "my lord") is an honorific title that used to refer to or address the eldest living brother of the king in the French royal court. It is also a customary French title of respect and term of address for a French-speaking man, corresponding to such English titles as Mr. or sir.
History
Under the Ancien Régime, the court title of Monsieur referred to the next brother in the line of succession of the King of France.
Hercule François, Duke of Anjou and Alençon (1555–1584), was the first notable member of the royalty to assume the title without the use of an adjoining proper name. In 1576, Monsieur pressured his brother King Henry III of France into signing the Edict of Beaulieu and effectively ending the Fifth Religious War of France. The resulting peace became popularly known as the Peace of Monsieur.
The...