Zeus kept it in secret, a project to recover his youth after his confrontation again Kronos. Not even the Ragnarok is stopping his untamed will, he's after all the youngest broth after Poseidon and Hades.

Once this were all done with a youth potion that'll definitely save him in a drink. His youthful appearance comes back, his energy, everything.. this will certainly shock everyone if he ever come out of this dark secret room.