The left one, the sadist, is the real one. The one on the right is a fake- someone else, most probably a female, pretending to be the protagonist, perhaps using illusion magic- and seems to be working (or forced to work) with the dark skinned male. The latter option 'past life' is obviously eliminated since the events happened a month later than the crucifixion of the princess. The former option would not make much sense because of a multitude of reasons that I would not be explaining- unless the author wants to deteriorate the series, which I doubt his objective would be. Because the two events are concurrent, a good explanation, considering the magical nature of the world would be this. However, I explain it this way, because I am void of emotions, and as such do not understand empathy. I could not understand the past version of the protagonist, but the current one seems fairly relatable to me- except for the magic part. If the author wishes to go with a neurotypical route, my explanations would be deemed incorrect, beware. As such, assuming that the author keeps things rational, the left person would be the protagonist.
Who is he? Twins? Past life???