Tritannus

Tritannus is the new enemy the Winx will face in Season 5. Not much is known about him except that he will become an ally of the Trix and was once a normal triton who was turned into a monster by pollution and whose goal is now to rule all the world and to conquer the Infinite Ocean. The Winx go underwater to fight him but their Believix powers are not enough and they will have to look for the Sirenix power and become Sirenix fairies.
From a recent trailer it was revealed that Tritannus is in fact Aisha's cousin.