In exchange for providing France with a large auxiliary force, Napoleon allowed Frederick to raise Württemberg to a kingdom on 26 December 1805. Friedrick was formally crowned king at Stuttgart on 1 January 1806, and took the regnal name of "King Frederick I". Soon after, Württemberg seceded from the Holy Roman Empire and joined Napoleon's Confederation of the Rhine. Once again, the assumption of a new title also meant territorial expansion, as the territories of various nearby princes were mediatized and annexed by Württemberg. As a symbol of his alliance with Napoleon, Frederick's daughter, Princess Catharina, was married to Napoleon's youngest brother, Jérôme Bonaparte.