[While making the movie] we talked about the fact that it was very likely [Scar and Mufasa] would not have both the same parents, Hahn said. The way lions operate in the wild
when the male lion gets old, another rogue lion comes and kills the head of the pride. What that does is it causes the female lions to go into heat [to reproduce], and then the new younger lion kills the king and then he kills all the babies. Now hes the new lion thats running the pride.
"There was always this thing about well, how do you have these two [male] lions? he continued. Occasionally there are prides that do have two male lions, in an interesting dynamic because theyre not equals [since they dont have the same parents]. One lion will always kind of be off in the shadows. We were trying to use those animal truths to underpin the story so we sort of figured Scar and Mufasa couldnt really be from the same gene pool."