The 1914 Willy-Nicky telegrams between the German Kaiser and the Russian Tsar to prevent the war were all in English. It wouldn't be surprising for a world leader to know English today following globalization, but how common or important was it for a sovereign to know English in the early 1900s?
Was the use of English in this case influenced by the fact that most of royal Europe was related through Queen Victoria? It would seem logical that English would be the preferred language "in the family".