Last Room Escape Puzzle

You wake up in a coffin.

You open the coffin lid to discover that you are in a strange candle lit room.

Getting out of the coffin and closing the lid you look around the room, noticing that all the walls are painted black.

On the wall behind you a silver cross is hanging. It seems to have no ill effect upon you.

On the wall opposite you, you see a mirror but, though you see the wall behind you, the coffin and the cross reflected in the mirror, you cannot see your own reflection.

To your right is a locked door and written on the door are the words, “My twin is unlocked”.

To your left is a locked door and written on the door are the words, “My twin is locked”.