The shortest reign of any monarch lasted just 20 minutes.
King Louis XIX of France holds an unfortunate record: the shortest reign of any monarch in history. Born Louis Antoine in 1775, he was technically king of France for a mere 20 minutes in 1830 following the abdication of his father, Charles X, during the July Revolution. The dauphin abdicated his right to the throne in the same document, which he signed 20 minutes after his father. (Legitimists — supporters of the Bourbon dynasty — didn’t accept this, and considered him the rightful king for the rest of his life.) On the other end of the world-record spectrum is Sobhuza II, whose 82 years and 253 days as both paramount chief and king of Swaziland make up the longest verified reign of any monarch in recorded history.
Some consider Louis XIX’s record to be a shared one, however. Luís Filipe, prince royal of Portugal, was fatally wounded in the same attack that killed his father, King Carlos I, on February 1, 1908, but survived 20 minutes longer. The 20-year-old was technically king for those few minutes, though he was never formally declared ruler. His younger brother Manuel II became the last king of Portugal on that fateful day instead. His reign wasn’t especially long, either: Portugal became a republic as a result of the October 5, 1910, revolution, and Manuel spent the remainder of his life exiled in England.