King Charles II suffered from rickets, impotence, and "a large head relative to his body size." And, according to Spanish researchers, it was all because of inbreeding.
The study, published in the journal Public Library of Science One, examined an extended pedigree including more than 3,000 members of the Spanish Habsburg family, over 16 generations. Of the eleven marriages made by six Spanish kings over this period, all but two were consanguineous and several involved very close relatives.
So inbred were the Habsburgs, that Charles II’s risk of inheriting a genetic disease was comparable with that of a child born to a brother and sister or father and daughter. [Link]