The original 5th prince drowned as a boy when he jumped into the water to save his dog, and the shadow (that was in his dog at the time) took over the drowned prince’s body. Remember how the maids said the dog was no longer in the palace? That’s because the shadow left the dog and went into Diez! (Ӧ ⌒ Ӧ｡) They can only inhabit bodies of the dead or else they will end up like Roselyn.
The why part is the memories we keep seeing about the race of people running and being hunted to extinction. You have to piece together the memories of shadow Diez and Macaron to get clues about what happened, but it’s not a full story yet. Hopefully, we will know what happened in the next season. (๑•ㅂ•)و✧
I am confused, is he the one that killed the original person in that body? What is his motive? Whyyyyy.