Goinkyo Maou-sama no Kaerizaki

Out of the blue, a bolt of lightning strikes an old man... but..! To his surprise, the lightning bolt rejuvenated him into a handsome man in his prime! His name is Gigi Alegarcia. He was called "stronger than the strongest" and "the man blessed with everything but magic"... the previous generation's Demon Lord himself.

(Source: Ganma!, translated)