Charles II of Spain was the result of nearly 200 years of inbreeding.

The House of Habsburgs stopped introducing new genes at around 1550, leading to a circular family tree.

Charles II had been born the son of an uncle-niece relationship, and historians Will and Ariel Durant described him as "short, lame, epileptic, senile and completely bald before 35, always on the verge of death but repeatedly baffling Christendom by continuing to live."

Before the age of six, Charles II had managed to survive an onslaught of diseases, which included chickenpox, measles, rubella, and smallpox.

He could not walk until he was 8 years old and could not chew food on his own. His tongue was so large that no one could understand what he was saying.

The nuncio papal Millini provided the following description of Charles II:

“The king is rather short, skinny, but not badly formed, only ugly in the face; he has a long neck, a long face, a long chin and as if it bent upwards; the lower lip typical of the Habsburgs; not very large eyes, turquoise blue and a fine and delicate complexion.

He has a look with melancholy on his face and a little astonished.

His hair is blond and long, and it is combed back so that the ears are exposed.

He cannot straighten, unless he leans against a wall, a table or something else.

His body is as weak as his mind. From time to time he shows signs of intelligence, memory and a certain liveliness, but not now; he usually looks slow and indifferent, appearing dumbfounded.

You can do whatever you want with him, since he lacks of own will."

Charles II's death in 1700 (at the age of 39) led to the War of Spanish Succession.

His autopsy report stated that his "heart was the size of a peppercorn; his lungs corroded; his intestines rotten and gangrenous; he had a single testicle, black as coal, and his head was full of water."