For these services he was created Duke of Gaeta by the king, and was assigned a pension of 20,000 lire by the Italian Parliament. In 1861 his intervention envenomed the Cavour-Garibaldi dispute, royal mediation alone preventing a duel between him and Garibaldi. Placed in command of the troops sent to oppose the Garibaldian expedition of 1862, he defeated Garibaldi in the controversial battle of Aspromonte. Between 1862 and 1866 he held the position of lieutenant-royal at Naples where he fought against the Brigandage in the Two Sicilies, and in 1864 was created senator.
On the outbreak of the war of 1866 he resumed command of an army corps, but dissensions between him and Alfonso La Marmora prejudiced the issue of the campaign and contributed to the defeat of Custoza. After the war he refused the command of the General Staff, which he wished to render independent of the war office. In 1867 he attempted unsuccessfully to form a cabinet sufficiently strong to prevent the threatened Garibaldian incursion into the papal states, and two years later failed in a similar attempt, through disagreement with Giovanni Lanza concerning the army estimates.
On 3 August 1870 he pleaded in favour of Italian intervention in aid of France, a circumstance which enhanced his influence when in July 1876 he replaced Costantino Nigra as ambassador to the French Republic. This position he held until 1882, when he resigned on account of the publication by Pasquale Stanislao Mancini of a despatch in which he had complained of arrogant treatment by William Henry Waddington. He died at Livorno in 1892.