The dispute between the Castroan and Spanish branches of the family began after the death of the last uncontested head of the house, Ferdinand Pius, in 1960.

Carlos married María de las Mercedes, Princess of Asturias, the heir presumptive of Spain, in 1901.

Although this renunciation was interpreted by some as removing Carlos and his descendants from the line of succession of the Two Sicilies, supporters of Alfonso argued that the renunciation would only have applied if Carlos's wife or an eventual son had actually become the sovereign of Spain, which did not happen and would have most likely not happened at the time of the signing regardless.

Interestingly, most of the other outspoken supporters of the Castro line were either sons-in-law of the Count of Paris or closely related to him.

In letters dated 21 July 2017, the Governor-General of Antigua and Barbuda issued a notice that the Duke of Castro's 2014 appointment to the Order of the Nation had been annulled.