The Fairy Type was announced for the first time during the E3 in June 11, 2013.
Fairy type is super effective against Dragon, Fighting and Dark and isn't effective against Fire, Poison and Steel. The Fairy type will be weak against Poison and Steel and resists against Fighting, Dark and Bug. It is immune to Dragon.
Sylveon is the first Fairy type Pokémon revealed.
Some old Pokémon will be reclassified as Fairy-type Pokémon:
Clefairy Clefable Jigglypuff Wigglytuff Mr. Mime Cleffa Igglybuff Togepi Togetic Marill Azumarill Snubbull Granbull Ralts Kirlia Gardevoir Azurill Mawile Mime Jr. Togekiss Arceus
(With Pixie Plate)