Which European royalty had the most hideous visual defects due to inbreeding. I believe it was Charles V, but I'm curious as to both the mental and physical deformities resulting from the inbreeding from the 12th to 19th centuries.
I don't know if he is the most inbred, but I think Charles II of the Hapsburgs could give everyone else a run for their money.
While Charles II suffered from severe mental disabilities, he also had his fair share of physical deformities. The Hapsburgs were well known for developing a slew of facial characteristics including; "prognathic mandible... a thick, everted lower lip, a large, often misshapen nose with a prominent dorsal hump, a tendency to flattening of the malar areas, and mild eversion of the lower eyelids."^1
There are also letters from some of the advisors in Charles' court that offer descriptions as well. One such letter to Louis XIV stated that, “The prince seems extremely weak, both cheeks have a herpes-type rash, the head is covered with scabs, and below the right ear a type of suppurating duct or drainage has formed. We have heard of this through other channels as the bonnet the child usually wears prevents seeing this area”^2
While I can't find any decent source for the autopsy notes for Charles II you'll usually find the notes quoted with something like, "a very small heart, lungs corroded, intestines putrefactive and gangrenous, three large stones in the kidney, a single testicle black as coal, and his head full of water.”
EDIT: I have not heard of the royal court or any other member of the Hapsburg family taking care to hide his deformities from the public. There were no procedures at the time for prognathism. When he was young, he did not attend school with other children. However, this has been attributed to his poor health as a child and his evident mental disabilities. Towards the end of his life, as his health deteriorated, the time he was able to be out of bed he was mobile and went for rides in his carriage. Unfortunately, he was only able to be out of bed for a few hours at a time so his public appearances were short.
Charles V of the Hapsburg line also suffered from some serious physical deformities, many of the sames one that afflicted Charles II of Spain. The Hapsburgs are probably the most extreme example of the physical and mental manifestations of severe inbreeding and unfortunate inheriting of dominant physical traits (someone with more knowledge of genetics can correct me and offer some knowledge on autosomal disorders) in Europe and the only ones I have any real knowledge of.
3: EAU15: The Spanish angle: Urological problems of Charles II (1661-1700)