He successfully managed the somewhat tense relations between the Spanish Borbóns and the newly restored French Bourbons, being honoured in 1815 as a knight of the Golden Fleece and made Duke of San Fernando Luis with the rank of grandee.

His next ambassadorial posting was to Rome, where he arrived just before the end of Pius VII's reign and was present during the conclave for the election of his successor as pope; he supported the efforts of Austria in favour of Cardinal Castiglioni's candidacy.

At Talleyrand's request, he dealt with unpleasant issues in London caused by his relatives, Louis, duc de Valençay and his father Edmond, duca di Dino, who had become addicted to gambling.

Declining to swear allegiance to King Louis-Philippe, the Duke and Duchess retired to the chateau de Montigny, where they received visitors, including Talleyrand.

The Duke died on 16 June 1837 and, having been predeceased by his son at Naples in 1819, his youngest brother Eugène succeeded to his French titles before they became extinct, whereas his Spanish ducado and grandeza devolved upon his elder daughter and her descendants.