King Leopold I of Belgium was born in Ehrenburg Castle in the Bavarian town of Coburg (Germany) on December 16, 1790 to Francis Frederick, the Duke of Saxe-Coburg-Saalfield and Countess Augusta Reuss-Ebersdorf zu Ebersdorf und Lobenstein. At the age of five he was named the colonel of the Izmailovski Imperial Regiment (Russia) and at the age of twelve (1802), he was already a general. A militaristic man, Leopold's work was put to use when Napoleon's troops invaded Saxe-Coburg in 1806, when Leopold was sixteen. Leopold left the Bavarian duchy for Paris the same year, where Napoleon offered Leopold the position of adjutant. But he declined the offer, and was overjoyed that he did so for his father, Duke Francis Frederick, died the same year and Leopold outranked his older brother, becoming the duke of Saxe-Coburg-Saalfield.

In England, Leopold's sister, Viktoria (Marie Luise Viktoria), had married Prince Edward Augustus, the Duke of Kent. On a visit to the kingdom in his early reign as  a duke, Leopold met the daughter of George, Prince of Wales, and his unfortunate wife, Caroline of Brunswick--Princess Charlotte Augusta.