How does one complete this quest? Is it necessary to slay the Grey Minotaur, or simply to fight him, then get the Gold Key?
A website I went to with a walkthrough claims retreating from the minotaur is sufficient, but even after getting the key, Lord Inspectron does not accept the quest as completed.

Never mind, I figured it out.

Seems I simply never went back to that room to register the message showing "The Lord of this Keep has been Defeated".

But thanks anyway.