Let me open this with a prelude: I studied medieval history in undergraduate and graduate school, and during that time, it was noted how royalty married royalty, to keep their bloodlines pure. Unsurprising. This often led, as with the Habsburg dynasty in Spain, to genetic physical deformities due to inbreeding. The Habsburgs developed prognathism, colloquially known as the Habsburg jaw, which can be clearly seen in contemporary portraits of royalty such as King Charles II of Spain, who was unable to chew due to his features.
Other times, this strict royal-breeding, through the centuries, developed other abnormalities. Below is Tsar Nicholas II of Russia (left), and his contemporary, King George V of England, in 1913. They were first cousins. Nicholas’s mother was the sister of George’s mother.
They look like identical twin brothers, not cousins.
To further emphasize this point, below is a picture of Tsar Nicholas II (left) and German Kaiser Wilhelm II (right), in 1907. Nicholas and Wilhelm were second cousins; Nicholas’s mother’s sister’s husband, King Edward VIII of England (and George’s father), was the brother of Wilhelm’s mother. Side note: Don’t worry, I’m also going cross-eyed trying to figure this out.
Though they don’t look identical, like above, they look strikingly similar for being relatively distant cousins.