That’s a bad plot twist. Rowan doesn’t show any signs of being a demon, either outwardly or spiritually. All his aspirations have always been to protect the world, and he fought in the previous war against the demon lord to protect people. He was one of the heroes blessed by the goddess. If he transforms from a human into a demon, that would be a good plot twist. But it would be a bad plot twist if he was born a demon. Too many questions would arise… Why doesn’t the goddess know about it? Why isn’t Rowan drawn to violence as a demon lord? Why are there no external signs on Rowan body? Why is no one still aware that Rowan is the true demon lord? Elves, dwarves, demons live for hundreds of years, but everyone lost sight of the demonic child, no one was aware?