On July 17, 2019, without any official announcement except a push notification, Niantic released their Legendary Raid Hour event to the world.
This event occurred all month in June featuring Kyogre and Groudon. The Pokemon that will be featured now will be Armored Mewtwo.
Players will notice that Armored Mewtwo raids will be available in every gym from 6 PM to 7 PM today. The event has already taken place across the international dateline.
Last week, Niantic did not announce whether or not Legendary Raid Hour would be taking place. It wound up not happening. PokemonGOHub reached out to Niantic before the event to confirm it would not be taking place on the 10th.
Trainers, we've confirmed with Niantic that Mewtwo will NOT appear more frequently during the previously mentioned Wednesday raid hours.— Pokémon GO Hub (@PokemonGOHubNet) July 6, 2019
The information has since been removed from the official website and now from our articles. Sorry for any confusion!