The brother of Deus appeared for the first (and last time) on the first dungeon island, only launched for FB version.
In each part of the dungeon island a brief story of Deus and his brother Darkus was told. There is not much info about him, only his appearance (blue pale skin and fire spitter) and that he created the demon dragon (probably cerberus too).
Since the Tree of Life advent, which brought a new deity to DC, I have some hope that the SP team will bring that character back or add him to some DC story. It would be very nice to see a new battle between Deus and his forgotten brother.