Leopold III (3 November 1901 – 25 September 1983) reigned as King of the Belgians from 1934 until 1951, when he abdicated in favour of the heir apparent, his son Baudouin. From 1944 until 1950, Leopold's brother, Charles, served as prince regent while Leopold was declared incompetent to rule. In 1950, the debate about whether Leopold could return to the throne provoked a political crisis known as the Royal Question
Leopold's reign as Belgian king was defined by his actions during World War II. Belgium had maintained a neutral stance in the conflict, but was invaded by the Wehrmacht on 10 May, 1940. Even after his ministers had left, Leopold remained in the country to lead his army in resistance against the invaders. Eventually the Belgian forces were overwhelmed. Leopold notified King George VI of the United Kingdom, by telegram on 25 May 1940 that Belgian forces were being crushed, saying "assistance which we give to the Allies will come to an end if our Army is surrounded". Two days later (27 May 1940), Leopold surrendered the Belgian forces to the Germans.
Prime Minister Pierlot spoke on French radio, saying that the King's decision to surrender went against the Belgian Constitution. The decision, he said, was not only a military decision but also a political decision, and the King had acted without his ministers' advice, and therefore contrary to the Constitution. Pierlot and his Government believed this created an impossibilité de régner:
Should the King find himself unable to reign, the ministers, having observed this inability, immediately summon the Chambers. Regency and guardianship are to be provided by the united Chambers.
It was impossible, however, to summon the Chambers at this time, and impossible to appoint a Regent. After the liberation of Belgium in September 1944, the Government would ask Leopold's brother, Prince Charles, to serve as Regent.
After Leopold's surrender, the British press denounced him as "Traitor King" and "King Rat"; the Daily Mirror published a picture of Leopold with the headline "The Face That Every Woman Now Despises'".
To avoid civil war in the midst of a violent general strike King Leopold III abdicated in favour of his son on 16th July 1951. He was Colonel-in-Chief of the 5th Royal Inniskilling Dragoon Guards.