12. Louis Antoine de Bourbon-Artois, Duke of Angouleme was King of France for less than 20 minutes.
The reign of Louis Antoine de Bourbon has to be one of the shortest in history. After the fall of Napoleon, France restored the ousted Bourbon dynasty as a constitutional monarchy. However, by 1830, the regime was once again in crisis due to the excesses of King Charles X- the younger brother of the executed Louis XVI. To save his family, Charles decided to bypass his legitimate heir Louis Antoine and abdicate in favor of his nine-year-old grandson, Henri Duc de Bordeaux. However, for Henri to become King, Louis also had to sign the declaration. He hesitated to do this for twenty minutes, during which time he was nominally King of France.