Well aside from you, he's the only person who has the key. It could be someone magic who stole it in an attempt to blackmail me, which really isn't anything new, but they would have revealed their hand by now. And I found out it was missing when I went to check on it a few days ago.

[ To see just how the sins of the past month or so reflected on his portrait because surprise! Dorian's a masochist! ]