In the original film, Simba was tricked into thinking he killed his father, a guilt ridden lion cub flees into exile and abandons his identity as the future King.
This isn't so much The Lion King 2, more of a prequel + sequel combined. With the voices of Aaron Pierre as Mufasa and Kelvin Harrison Jr. as Taka, plus all the usuals: Seth Rogen as Pumbaa ...