Setting: Just before the coconut scene in the first movie. Nuka walks in to find his father lying on his back sleeping.
Nuka: Hey dad, I just overheard mom talking to a hyena. She said you killed my uncle!
Scar: Oh, I knew this day would come soon. Yes, Nuka, I did kill your uncle, and your cousin too.
Nuka: Why?
Scar: Well, when I was about your age, my father told the pridelands that Mufasa would be king. I was happy for him at first, but after that announcement, no one payed attention to me. Then, when we grew, your cousin Simba was born. That meant that if Mufasa died, Simba would become king, not me. So, I lead your cousin into the gorge and had the hyenas start a wildebeest stampede. Mufasa put Simba on a ledge and climbed a rock to the top where I was waiting. I threw him back in and made the hyenas kill your cousin.
Nuka: So...your a murderer?
Scar: Oh, murderer is such a strong word! Think of it as pushing your way to the top.
Nuka: Do you think when I'm older I'll want to kill Kovu?
Scar stood still, watching his young son.
Scar: I think it would be best not to talk about this anymore. Now you run along now and have fun, and remember...it's our little secret!
-ScaЯ
(characters not mine)