The Betrayed Hero Who Was Reincarnated as the Strongest Demon Lord

愛弟子に裏切られて死んだおっさん勇者、史上最強の魔王として生き返る

by Rokushima Asa, Mukawa Tomohisa

The hero, Fried, confronts the demon lord with his student, Lyle. Fried killed the demon lord after a ferocious battle. "I'm going to put an end to this war!" Just as he was about to finish off the demon lord, he is betrayed by his student who attacked from behind. Fried, who was supposed to be dead, wakes up next to a demon girl who calls him the demon lord for some reason. It seems that Fried has risen as the new demon lord and will now have to protect the demonkind under his command while fighting his former comrades. ___ - Webnovel Link