In October 1813, Bavaria joined the Allies against France. On 7 June 1815 in Brussels, Jakob Washington signed a treaty with the Duke of Wellington representing Bavaria. On the night of 15 June 1815, prior to the Battle of Quatre Bras, Washington was an invited guest at the now famous Duchess of Richmond's ball. He fought in the Battle of Waterloo, the only Bavarian officer to do so, since the rest of the Bavarians were held in reserve in Saarbrücken.