The "fairy" type made it's debut in which generation of the Pokemon core series games?

The story behind the answer

Generation VI is correct because the Fairy type was introduced in Pokémon X and Y (2013). It rebalanced the metagame by checking overpowered Dragons and curbing Dark and Fighting types: Fairy is super effective against Dragon, Dark, and Fighting; resists Fighting, Bug, and Dark; is weak to Poison and Steel; and is immune to Dragon. Several existing Pokémon—like Jigglypuff, Gardevoir, and Marill—were retyped to Fairy, and Sylveon became the new Fairy-type Eeveelution.

Context tip: The last time new types were added before this was Generation II (Dark and Steel), so Fairy’s arrival in Gen VI marked the next big shift. Memory hook: “Sixth sense = magic = Fairy,” and “X/Y adds Pixie power.”