The Lion King 3: The Lost King

Simba and Nala had a son before Kiara. Kopa. But Zira soon caught Kopa with Vitani and grew angry. She threatened to kill Kopa unless he left the Pride Lands forever. Kopa soon left, and after a year of travel, took over a Pride. There was a little lion cub there, one that was a son of the former leader. Kopa, remembering his lessons from the Pride Lands, spared the cub's life. But this decision could lead to the end of Kopa and his entire Pride.