How is he VI? There was only one king of Naples/Sicily bearing that name before him, so Conrad IV of Germany. But his number "IV" refers to German throne and the dukedom of Swabia, not to Neapolitan/Sicilian royal status. And his son, Conradin wasn't neither king of Germany nor Naples/Siciliy so why should descendants of Charles d'Anjou even COUNT him? Conrad would be Conrad II, as a king of Naples.
My bad. This is what happens when you're typing after midnight and you're too lazy to fact check.
Thanks for catching it