Prince or Princess of Asturias is the main substantive title used by the heir apparent, heiress apparent or heir presumptive to the throne of Spain. According to the Spanish Constitution of 1978:Article 57 [...]
2. The heir apparent, heiress apparent or presumptive, from birth or event that makes him such, will have the dignity of Prince of Asturias and other titles traditionally linked to the successor of the Crown of Spain.