Thanks to leaks from the latest issue of the Japanese magazine CoroCoro, we finally know the two legendary Pokémon for Ultra Sun/Moon. As many fans suspected, it is indeed the result a fusion between Necrozma, star of this opus, and Solgaleo and Lunala.
We don't know much but we know that the name of these fusions would translate to "Necrozma Mane of Twilight" for the union with Solgaleo, and "Necrozma Wings of Dawn" for the one with Lunala. These hybrid creatures will also keep the signature moves of Solagelo & Lunala: Sunsteel Strike and Moongeist Beam.
We'll know for sure when Pokémon Ultra Sun & Ultra Moon is released on November 17th on 3DS.