Question - is Bradley James secretly the Tenth Doctor, or is David Tennant secretly King Arthur? Obviously, King Arthur can't be Ten, as Old School has actually established that the Doctor is Merlin (there were hints about Ace being the Pendragon, but that can be explained by inheritance.) But Ten could have bleached his hair and passed himself off as King Arthur to rescue that kid from Midnight and Reinette's friend from Girl in the Fireplace from whatever mind-control ray is holding them in the Incredibly Anachronistic Middle Ages.