Why did a rabbi circumcise King Charles when he was a baby?

There is a very old conspiracy theory that the British royal family are heirs to the throne of the Biblical King David and that they consequently maintain certain Jewish traditions

There is something about the British royal family which seems to attract those inclined to believe strange ideas and bizarre theories. David Icke, the leader of a cult in Britain, famously claimed that Queen Elizabeth and Prince Philip were shape-shifting lizards from outer space, but this is by no means the most peculiar notion to be associated with the family. Since the nineteenth century, there have been those who claim that the heirs of King David, whose story is told in the Old Testament of the Bible, now sit on the British throne and that King Charles is actually the hereditary ruler of Israel, as well as that of Britain. Some find confirmation of this outlandish version of history in the indisputable fact that when King Charles was born in 1948, his parents summoned a rabbi to Buckingham Palace to circumcise their first-born son.