The Habsburg Kings of Spain descended from Queen Joanna "The Mad" of Castile (1479-1555), who was mentally unstable and prone to fly into rages. Her descendants increased her inheritance by inbreeding: they preferred to marry either their cousin or their niece. These incestuous marriages resulted in the mentally and physically handicapped King Charles II (1661-1700), who possessed the physical peculiarities of the Habsburgs to an extent that made him little short of a monstrosity.
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Charles II of Spain was the result of generations of inbreeding within the Habsburg family. His mother was a daughter of his father's sister who had married her cousin the Emperor Ferdinand II. His great-grandfather, Philip II of Spain, too, had married a daughter of his sister who had married her cousin the Emperor Maximilian II. As a result, Charles II of Spain descended multiple times from Joanna "The Mad" as shown below.
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The ancestors of Charles II often married either their cousin or their niece |
Sources:
- Bos, J.N.W.: Mad Monarchs: Carlos II of Spain
- Khan, R.: Inbreeding & the downfall of the Spanish Hapsburgs