I recently rewatched (and enjoyed again) the British political satire To Play the King. In it, a young prince (clearly patterned after the current Prince William) becomes King. He’s still a minor at the time, so I assume there would be a regency.
British history gives us a mixed bag of regencies of young kings. Their length usually seemed to depend upon the political situation of the day; sometimes regents were reluctant to yield power to their youthful sovereigns. Hey, it’s only human nature! Henry III’s regency ended when he turned 20; Edward III’s, at 18; and Henry VI’s, at 16. The young Edward V, age 13, disappeared in the Tower along with his younger brother, perhaps done in by order of their uncle and “protector,” Richard III. Edward VI died at 15, having never ruled on his own.
Under current British law, when would a young prince or princess reach adulthood and be able to reign? Or would Parliament have to pass a law tailor-made for the situation when and if it arises?