Charles III

Charles III was the King of the United Kingdom who succeeded Elizabeth II. Charles III was succeeded by William V. When the Doctor found that Edward VII had dissapeared along with Balmoral Castle in 1902, he warned that the future of the royal family, along with the rest of history, was threatened. Saying that, along with the rest of his successors, there would be no Charles III. (NSA: Revenge of the Judoon)

Behind the scenes

 * Charles is likely the unnamed King mentioned in DW: Battlefield. In a period during the 1990s when Elizabeth was temporaily off the throne.