The youngest king in history wasn’t even a day old!
The youngest (and possibly most adorable) king ever was Alfonso XIII of Spain, who was crowned the ruler of Spain on the day he was born (side note: best birthday present ever). The reason for this is that his father had had died a year before his birth. The French newspaper Le Figaro described the young king as “the happiest and best-loved of all the rulers on Earth.”
Alfonso didn’t have to take care of any serious duties as a kid. His mother was appointed regent during his minority. However, on his 16th birthday, he assumed control of the state (again: best birthday present ever).