What’s In a Name: On This Day in 1917
After three ghastly years of war with cousin Willy, the royal family of Britain felt pressured to change its name. Saxe-Coburg-Gotha sounded unpatriotic. Indeed, the British royal family was quite German. Although born in London, Queen Mary was Teck-nically German. The mother of King George was (mercifully) Danish, but his paternal ancestry was almost completely Deutsch. (There had been a Scottish/Danish great- great- etc. grandmother almost three hundred years earlier.) The family decided to rename itself the impeccably anglophile guise of Windsor.
I have done a calculation of the British ancestry of the Royal family. You may need a microscope.
George V was 3/32768 English. By comparison, he was much more Scottish: 3/4096. The rest of his ancestors were German or Danish. However, George VI actually married a nice British girl. But then his daughter had to marry ein Battenberg (even if the family tactfully translated it to Mountbatten).
It is ironic but British law does not require the monarch to be British. The sole requirement is that he or she be Protestant. At the penalty of disinheritance, a member of the Royal Family is prohibited from marrying a Catholic.
However, the prohibition does not apply to other religions. So, in theory, Prince Charles could have married Nigella Lawson (Levinson actually) or Rachel Weisz.