The colt Pokemon will be the first of three revealed event creatures.
Keldeo will be the first "new" legendary revealed, as leaked in early images from the upcoming issue of CoroCoro magazine.
Although the Pokémon's existence was known beforehand alongside two others (full data about all event creatures exist inside of the games' coding), the article acts as the first official confirmation. Keldeo, the colt Pokemon, leads the Musketeer trio, which includes Cobalion, Terrakion, and Virizion.
The magazine also revealed the new title of the upcoming Pokémon movie, which is to be called Kyurem Vs. The Sacred Swordsman - Keldeo.
Distribution methods for the event Pokémon have not been revealed.
Image from CoroCoro