Duke of Calabria was the traditional title of the heir apparent of the Kingdom of Naples after the accession of Robert of Naples. It was also adopted by the heads of certain Houses that had once claimed the Kingdom of Naples in lieu of the royal title.
There are at present two claimants to the title of Duke of Calabria. In the Spanish context, it is the title for the head of the House of Bourbon-Two Sicilies, and in the Italian context it is the title for the heir to the Duke of Castro, the head of the Royal House.
As royal title for the heir apparent to the throne:
As customary title of the head of the House:
As customary title of the claimant to the headship of the House:
As customary title for the heir of the claimant to the headship of the House: