My fault Russia was allied with Britain, but the royal families were so inter-related back then.
I don’t believe you were wrong “first cousins” - I believe Kaiser Wilheim was in Germany.
The end of World War I bringing about the fall of the Royal houses of Russia and Germany both would lead to extraordinary carnage in the years to come. The concept of “royalty” is one thing to discuss academically, but it is far less likely had in that particular point in time those royal houses remained intact that we would have ended up with the tens of millions of deaths resulting from Nazi Germany and the Soviet Union.
It was France that was allied with Russia. Britain was aligned with Belgium, and that’s what brought the Brits into the war.