I've been watching the movie "King Arthur", and I heard Arthur asking "Which is X?"
Is it correct to say "Which is Jay?" instead of "Who is Jay?"?
"Which is Jay" and "Who is Jay" mean completely different things.
Isn't the King's English always correct, by definition?
Of course, Arthur, had he existed, would not have been speaking English but British -- the P-Celtic language Brythonic -- so we can blame the translator if necessary.