so, we got several versions of Kopa here. The short tempered sissy, the cub simba will never figure out isn't his, and scar junior
but to be honest with you, in my headcanon Ni is Kopa's father. I mean, if you compared Ni and Simba appearence wise, they're pretty similar. Golden coats, red/brown eyes, even the shape of their nose and eyes are the same. All accept for the manes of course. So either way, Simba would never figure it out.