Simeon of Saxe-Coburg-Gotha was born in 1937. From the death of his father, Tsar Boris III, on August 28, 1943, until September 15, 1946, he was Tsar of Bulgaria under the name Simeon II, but due to his age, he ruled the Regency Council on his behalf.
After the death of Elizabeth II, he is practically the third oldest monarch in Europe. In reality, he never abdicated the throne, unlike the kings of Serbia, Romania and Greece, who abdicated after World War II.
On September 15, 1946, in the presence of the Allied Control Commission (ACC) and parts of the Soviet Army, a Referendum was held to declare Bulgaria a republic. Over 95% of those who voted were in favor of a republic, but since the country was still effectively occupied by Soviet troops at the time, the referendum vote did not meet modern understandings of a free vote.
On September 16, 1946, the royal family (Queen Joanna, Simeon II and his sister Maria-Louise) was expelled from the country. Thus Simeon of Saxe-Coburg-Gothic left Bulgaria without ever having abdicated the throne. Some believe that the referendum is unconstitutional and illegitimate, because it was not held in accordance with the current Tarnovo Constitution, which did not foresee a change in the form of government.
If Bulgaria had not been declared a republic, Simeon II would have improved the world record for governance. He ascended the throne on August 28, 1943. This would make him over 74 years, longer than the reign of France’s “Sun King” Louis XIV of 72 years and 110 days. Elizabeth II is second in this ranking with 70 years and 214 days.