New head-canon!
When Taka came of age, he left home to find a pride of his own. Mufasa regularly heard from his brother and how he was doing. Then word stopped. Mufasa looked out every day for Taka's Majordomo, but they never came.
One day, Mufasa stood outside the cave as usual, when he caught the scent of blood on the wind. It was Taka! He was limping, covered with blood.
"We..we were totally unprepared" He rasped "Everyone is gone" He said before collapsing.
Mufasa took Taka in, who he jokingly called Scar. Taka "Scar" was grateful for his brothers charity, but it soon turned sour. Mufasa expected too much and would constantly remind him of his good deed. It didn't take long for Scar to resent his brother and turn into scar for real!