Personal details Charles was the only surviving son of Mariana of Austria (1634–1696) and Philip IV of Spain (1605–1665) who was 56 years old at the time of his son's birth. For political reasons, marriages between Spanish and Austrian Habsburgs were common; Philip and Mariana were  uncle and niece. All four of his grandparents were descendants of Ferdinand I, Holy Roman Emperor and Anna of Bohemia and Hungary. All eight of his great-grandparents were descendants of Joanna and Philip I of Castile. All sixteen of his great-great-grandparents were descendants of Ferdinand I of Aragon and Eleanor of Alburquerque
Personal details Charles was the only surviving son of Mariana of Austria (1634–1696) and Philip IV of Spain (1605–1665) who was 56 years old at the time of his son's birth. European nobility commonly married within the same extended family to retain property, although the Spanish Habsburgs were unusual only in the extent. Of eleven marriages contracted between 1450 and 1661, the vast majority contained some element of Consanguinity, while Philip and Mariana were one of two between uncle and niece. 
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For political reasons, marriages between Spanish and Austrian Habsburgs were common;
European nobility commonly married within the same extended family to retain property, although the Spanish Habsburgs were unusual only in the extent. Of eleven marriages contracted between 1450 and 1661, the vast majority contained some element of Consanguinity, while
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one of two between
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All four of his grandparents were descendants of Ferdinand I, Holy Roman Emperor and Anna of Bohemia and Hungary. All eight of his great-grandparents were descendants of Joanna and Philip I of Castile. All sixteen of his great-great-grandparents were descendants of Ferdinand I of Aragon and Eleanor of Alburquerque