Prince Ranieri Maria Gaetano, Duke of Castro (3 December 1883 – 13 January 1973) was a claimant to the headship of the House of Bourbon-Two Sicilies.

He was born in Cannes, France the ninth child but fifth son of Prince Alfonso, Count of Caserta and Princess Maria Antonietta of Bourbon-Two Sicilies (1851–1938). Ranieri for a time served in the Royal Spanish Army.

Following the death of his brother Prince Ferdinand Pius, Duke of Calabria on the 7 January 1960 Prince Ranieri was declared Head of the House of Bourbon-Two Sicilies by all relatives except for Infante Alfonso, Duke of Calabria and his children, because the Infante's senior branch of the family abdicated their claims in order to be in line for the Spanish throne. He remained head of the house until his death on 13 January 1973 in Lacombe. He handed over the functions associated with the headship of the house to his son in 1966.

Ranieri married his cousin Countess Maria Carolina Zamoyska (1896–1968) on 12 September 1923 in Vyšné Ružbachy, Slovakia, from the marriage he had two children:

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