Berthier bequeathed Grosbois to his sister before leaving for the Army and World War I on 1 August 1914. An army captain and the leader of a company of chasseurs during the Third Battle of the Aisne, he sustained wounds from shell fire at Fort de Condé-sur-Aisne and died from them on 30 May 1918. He had no issue. He was buried at the Château de Grosbois like his father and grandfather.