Frederick Charles Louis Constantine, Prince and Landgrave of Hesse, was the brother-in-law of the German Emperor, Wilhelm II. He was elected King of Finland on 9 October 1918, but renounced the throne on 14 December 1918.

The Kingdom of Finland was a failed attempt to establish a monarchy in Finland in the aftermath of the Finnish Declaration of Independence from Russia in December 1917 and the Finnish Civil War from January–May 1918. The victorious Whites in the Parliament of Finland began the process of turning Finland into a kingdom and creating a monarchy. Although the country was legally a kingdom headed by a regent for over a year, the king-elect Friedrich Karl never reigned nor came to Finland following Germany's defeat in World War I. Republican victories in subsequent elections resulted in the country becoming a republic.