Originally Posted by Rodion Romanovich
It's a recessive X-linked genetic disorder, and those have a tendency to be much more common after inbreeding than after anything else, because the female needs to have at least one recessive allele. Besides, it's a well known fact that most of the kings and queens of European countries in the 18th, 19th and 20th centuries were inbred because of the many diplomatic marriages. I'm sure you can find a graph on google showing how cousins or children of cousins or similar would marry and have children several times, and after doing this for a few generations, the Romanov heir got problems. There was some article about this a few decades ago. Naturally you can get hemophilia without inbreeding as well.