It’s quite a fun story of various dynastic marriages and changing family names in Europe over the course of a few centuries. The Glorious Revolution in 1688 saw the last Stuart King of England and Scotland, James II and VII, deposed due to his Catholicism. He was in turn replaced by his Protestant daughter, Mary II and her husband William of Orange. These two are the William and Mary for which the College of William & Mary is named. After their reign, their daughter Queen Anne died without an heir, and so under the new succession laws of the now United Kingdom, the throne passed to her second cousin, the Duke-Elector of Hanover, George I, thus beginning the Hanoverian Kings. The Hanoverians would reign up through the death of Queen Victoria in 1901, including King George III of American Revolution fame. At this point, the throne is held by a distinctly German dynasty. Now, Queen Victoria’s husband, Prince Albert, hailed from one of the many small German polities within the German Confederation: the Duchy of Saxe-Coburg und Gotha, and his house shared that name. Thus, when the throne passed to Victoria’s son, King Edward VII, the ruling house changed as well from the House of Hanover to the House of Saxe-Coburg und Gotha.

Now, from the coronation of Edward VII at the turn of the century, we fast forward a few years to 1914 and the outbreak of World War I, where the United Kingdom is fighting the German Empire. Anti-German sentiment was strong in the UK, and there was substantial fear of German infiltrators or invaders. Not even the Royal family and nobility were above suspicion, as even their loyalty was called into question. In response to this, multiple British families changed their family names to be more “English”. Prince William of Battenberg, First Sea Lord at the start of the war—who was forced out of his position in part of these anti-German feelings—would change the family name to the more English “Mountbatten” (yes, that one). The Royal family, in addition to relinquishing their German titles and dignities, would change their name to the House of Windsor in 1917, as raids by German Gotha bombers increase anti-German sentiment, while also further highlighting the tie of the Royal family’s name to the German enemy. “Windsor”, in turn came from the town of Windsor and Castle Windsor, both strongly tied to England and the monarchy.

Had to write this on mobile, so apologies for typos. This isn’t my main topic area, but please feel free to ask any follow ups and I’ll try to answer. Hope this helps answer your question!