I remember that when they revealed the Pokemon in gen 4 and gen 5, they never made a big deal about discovering what type it is. But now if you go to the official page (http://www.pokemon.com/pokemonxy/en-us) they state that:
"Experienced Pokémon Trainers know that Eevee can evolve into seven different types, and now a new Eevee evolution with a different type has been revealed! What type is Sylveon? You'll have to wait to find out! Stay tuned to Pokemon.com for more news."
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