This room's layout is strangely similar to the room where Plague Knight finds the Phase Locket. The chest is also on the same spot.

This is the same room, if you finish Specter of Torment you'll understand.

I already finished it when I said that, but I found it strange that the room where Specter Knight hid the locket in the end is the one where Plague Knight found it, meaning Specty's room's background is already gone. What exactly is that supposed to mean ? That his room was already destroyed near the ending of Specter of Torment ?