He Gets Abandoned From His Kingdom, So He Becomes A Overpowered Villain

The hero was the one who saved all of humanity by defeating the Demon Lord.
Everyone was grateful, but there was one person who was very afraid of Leo's power: the king.
The king became so scared, that he chose to betray him.
He banished Leo from the kingdom.
This betrayal made Leo angry, and he decided that he would get revenge by joining forces with the very demons he had once fought.
Anime: On Comment Section