He was born in Paris, officially the son of Marshal Alexandre-Sébastien, comte de Flahaut who was guillotined at Arras in February 1793, by his wife, Adélaïde Filleul, However, Charles de Flahaut was generally recognized to be the offspring of his mother's liaison with Talleyrand, with whom he was closely connected throughout his life. His mother took him with her into exile in 1792, and they remained abroad until 1798, moving from England to Switzerland, before Hamburg where she met her second husband, Ambassador DomJosé Maria do Carmo de Sousa Botelho Mourão e Vasconcelos, :pt:Morgado de Mateus|5.º Morgado de Mateus. Charles de Flahaut volunteered for military service joining the cavalry in 1800, and received his army commission after the Battle of Marengo. He was appointed aide-de-camp to Joachim, 1st Prince Murat, and was wounded at the Battle of Landbach in 1805. At Warsaw he met Anne Poniatowska, Countess Potocka with whom he quickly became intimate. After the Battle of Friedland he was awarded the Legion of Honour and returned to Paris in 1807. He served in Spain in 1808, and then in. Meanwhile, the Countess Potocka had established herself in Paris, but Flahaut had by this time entered into a relationship with Queen Hortense of Holland; the birth of their son was registered in Paris on 21 October 1811 as Charles-Auguste-Louis-Joseph Demorny, later created Duc de Morny. Flahaut fought with distinction in the Russian Campaign of 1812 and, in 1813, was appointed Brigadier-General and aide-de-camp to Emperor Napoleon being promoted, after the Battle of Leipzig, as a Général de division. After Napoleon's abdication in 1814 he submitted to the new French government, but was placed on the retired list in September. Flahaut was assiduous in his attendance on Queen Hortense until the Hundred Days brought him back into active service. A mission to Vienna to secure the return of Empress Marie-Louise resulted in failure. He was present at Waterloo, and afterwards sought to place Napoleon II on the throne. He was spared exile due to an intervention by Talleyrand, but was placed under police surveillance. Flahaut then chose to leave for Germany, and thence to Britain. The Flahauts returned to France in 1827 and, in 1830, King Louis-Philippe promoted the Count to the rank of Lieutenant-General as well as creating him a Peer of France. He remained a staunch supporter of Talleyrand's policies, and in 1831 served briefly as French Ambassador to Berlin. Subsequently, he was attached to the household of the Duke of Orléans and, in 1841, was posted as Ambassador to Vienna, where he remained until 1848, when he was dismissed and retired from army service. After the Coup d'état of 1851, his services were re-engaged, and from 1860 to 1862 he served in Britain as French Ambassador to the Court of St James's. In 1864, the Flahauts returned to Paris and took up residence at the Hôtel de Salm, when Charles was appointed Grand Chancellor of the Legion of Honour. He died in Paris on 1 September 1870. In the opinion of the unnamed author of a biography on Flahaut in the Encyclopædia Britannica Eleventh Edition: "The comte de Flahaut is perhaps better remembered for his exploits in gallantry, and the elegant manners in which he had been carefully trained by his mother, than for his public services, which were not, however, so inconsiderable as they have sometimes been represented to be".
