 Decaen made an unsuccessful effort to maintain the royal authority in that city after the return of Napoleon I from Elba in 1815.After the royal princes had left France, Decaen rejoined the emperor's side and during the Hundred Days, he commanded troops in the south of France, for which he was imprisoned for five months after the Bourbon restoration which occurred after Waterloo.After his release he retired to civil life until he was recalled to activity by Louis-Philippe I in 1830.