well, most of the royal families of Europe are related to each other -- you know that the King of England, the Tsar of Russia and the Kaiser of Germany in WWI were all first cousins? All had the same grandma -- Queen Victoria?
And memebers of the Saxe-Coburg-Gotha's (the real name of the Windsor family) include Kings of Bulgaria etc.?
Didn’t know that one specifically although familiar with the practice of having royalty interwed across nations.