Fairy was the new Pokémon type introduced in Generation VI. It debuted in Pokémon X and Y, released for the Nintendo 3DS in 2013.
The Fairy type was added to expand the battle system and provide a strong counter to Dragon-type Pokémon. Several existing Pokémon, including Clefairy and Jigglypuff, were reclassified as Fairy-type or gained Fairy as a secondary type.
Dark and Steel were introduced together in Generation II, making them common alternatives in this question. Dragon was already present from Generation I. Fairy was the first new type added since Generation II, bringing the total number of types to 18.