Born in Caserta, Alfonso was the fourth-in-line heir to the throne of Two Sicilies since the time of his birth. Ahead of him in line were his older half-brother Francis and older brothers Prince Louis, Count of Trani and Prince Alberto, Count of Castrogiovanni.

On 12 July 1844, Alberto died. He was two months short of his fifth birthday and naturally childless. Alfonso became the third-in-line heir.

On 22 May 1859, Ferdinand II died. Francis became King but had no children yet from his wife Maria Sophie of Bavaria. Louis became his Heir Presumptive and Alfonso the second-in-line heir to their half-brother.

However the Two Sicilies were conquered by the Expedition of the Thousand under Giuseppe Garibaldi in 1861. Garibaldi served the Kingdom of Sardinia which was in the process of Italian unification. The deposed Royal House survived with Francis still at its head.

On 8 June 1886, Louis died. His only daughter Princess Maria Teresa was not in line for the throne because females were barred from succession. Alfonso became the heir presumptive to Francis who had survived his own daughter.

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