Somerset also saw action during the Hundred Days: he served on Wellington's staff at the Battle of Quatre Bras on 16 June 1815 and at the Battle of Waterloo two days later (where he had to have his right arm amputated and then demanded his arm back so he could retrieve the ring that his wife had given him). Promoted to colonel and appointed an aide-de-camp to the Prince Regent on 28 August 1815, he was appointed a Knight of the Bavarian Military Order of Max Joseph on 3 October 1815. He remained with the Army of Occupation in France until May 1816 when he returned to the post of secretary at the British Embassy in Paris.