What is the ruling on a great-grandfather intentionally killing his great-grandchild?

A grandfather killing his grandchild is forbidden and a grave sin. It is condemned by Allah’s saying: "And whoever kills a believer intentionally, his recompense is Hell to abide therein, and Allah has condemned him and cursed him and prepared for him a great torment." However, according to many scholars, a grandfather is not to be killed for (killing) his grandchild, because he is like a father.