The shortest reign in history lasted only twenty minutes.
Why it is true
Louis XIX of France was technically king in 1830 between the time his father abdicated and the time he himself signed his own abdication.
Source: British Museum
Would you rather be asked first?
This is the reading side of the site, so the answer is in the sentence above — that is the whole point of it. Test yourself works the other way round: the question comes on its own, and the fact and the explanation only appear once you have answered.