feebas evolves with maximum beauty. ^_^
Anyway, to evolve Feebas into Milotic, your Feebas has to have its max beauty, then after that level it up by 1. And then Feebas will evolve into Milotic.
When it's friendship rating is maxed out or in Black and White, when you trade it with a prism scale.
You got to level up feebas with high beauty.