How do you evolve feebas in Pokemon X and Y?

Question

I want Milotic and Im thinking of trading a Machop for a Feebas, but I dont know how to evolve it once I have it in X. Does anyone know how to do that?

Answer 1

You trade one that is holding a Prism Scale.

Source. (it says gen 5 but it applies to gen 6 too)

Answer 2

It evolves into Milotic when leveled up with its Beauty condition high enough or when traded holding a Prism Scale (Generation V onwards).

Source