A lot of American comedians love to joke about how the royals are all seriously inbred. There seems to a perception that even modern-day royals are so inbred that they contain massive amounts of genetic defects. Certainly, this occurred in the past, but nowadays royal families are generally trying to avoid too much consanguinity. However, in the case of Charles III there is indeed some inbreeding.
Examining the ancestry of the current monarch of the United Kingdom, King Charles III.
Charles III parents, Queen Elizabeth II and Prince Phillip were both third cousins and second cousin once removed. Queen Elizabeth’s great grandfather, Edward VII, was a brother to Princess Alice, who was Prince Phillip’s great grandmother; this makes them third cousins.
Additionally, Prince Phillips grandfather, King George I of Greece, was a brother of Princess Alexandra of Denmark who was the wife of Edward VII and therefore Elizabeth’s great grandmother. This makes Elizabeth and Phillip 2nd cousins once removed as well.
What this means is instead of having 32 great-great-great-grandparents, Charles has only got 30. And instead of having 62 ancestors going back 5 generations (2 parents, 4 grandparents, 8 great grandparents, 16 great-great-grandparents, 32 great-great-great-grandparents), he only has 58. And things only get worse from then on going further backwards.
Amongst those ancestors, there are quite a few other overlaps that occur. Famously, Queen Victoria and Prince Albert were first cousins. Also. Mary of Teck, who was married to George V, was descended from George III and thus they were second cousins once removed. Another example, Prince Alexander of Hesse and by Rhine’s parents were second cousins. Thus, going back 7 generations, instead of 254 ancestors, the King only has 196.
The coloured squares are persons in Charles III that appear more than once. The light grey squares are parents of people who appear more than once.
However, not that all of Charles’ ancestors were royalty. For instance, there were many commoners on the maternal side of Elizabeth Bowes-Lyon, better known as the Queen mother. So going back 7 generations one of the king ancestors on the Windsor side is only known by her first name (Elizabeth, wife of John Walsh).
Also on Prince Phillips side, there is one of the Kings’ ancestors 7 generations back who’s name is completely unknown (the wife of Markus Kornély whose parentage is also unknown). Anyone who has researched family history knows you run into dead ends on family trees and that happens when researching the family history of monarchs too.
Thus King Charles is only mildly inbred compared to what used to happen.
Charles II of Spain – The poster child of inbreeding
Charles II of Spain was the last Habsburg monarch of Spain in the late 1600s. This was because he wasn’t able to breed, despite being married twice, as he was horrible deformed by decades of inbreeding that left him both physical and mentally disabled.
Part of the reason he was so inbred was because his father, Philip IV, had married his niece. Phillip probably did not think this was abnormal as both his grandfathers had married their nieces (at least his parents were only first cousins). Charles II tree contains so many overlaps that going back 7 generations, instead of 254 ancestors, he only had 84.
Each Coloured square represents a person who appears more than once on this family tree. Light grey squares represent parents of people who appear more than once. The square containing the star represents another daughter of the Purple and Gold couple.
The reason for such extreme interbreeding is that the Spanish royals could only marry suitable people of the correct rank. Since the Protestant Reformation, there were only a few Catholic royal families of high enough rank for the family’s standard. And because France was often an enemy, the Austrian and Spanish Habsburg families just kept interbreeding.
(Interestingly, in Episode 5 of Season 4 of “Succession”, one of the Swede’s made a joke in Swedish about Cousin Greg being as inbred as the Habsburgs, but I suspect that joke was written by an American.)
So in comparison to old Charlie Habsburg of Spain, our modern day King Chucky has quite a diverse genetic profile.