Frederick William III of Prussia
At first Frederick William tried to follow a policy of neutrality in the Napoleonic Wars. But in the end he entered into war in October 1806. On 14 October 1806, at the Battle of Jena-Auerstädt, the French defeated the Prussian army, and it collapsed.  The royal family fled to East Prussia, where  Emperor Alexander I of Russia (who, rumour has it, had fallen in love with Queen Louise) helped them against Napoleon.