Update: Niantic has officially announced the Legendary Lake Trio as the new regional Raid Bosses. With that being said, the tweet from Pokemon Go Espana (Spain) account was a false alert.
For more info about the regional Raid Bosses please visit this link.
Previous Story: Trainers, it seems like the Normal Type Legendary Pokemon from Gen 4 Regigigas could be the next Legendary Raid Boss in the game.
Pokemon Go Spain Twitter account shared the following:
Attention Trainers, the leader of the Regis is on the way and wants to test your strenght. The collosal Regigas is coming to Raids and will be available to battle and catch until May 28 at 1:00 PM PST.
Their tweet was deleted immediately, but some players made a screenshot and you can take a look below.
At this moment nothing is officially confirmed, so please take this with a grain of salt. We will follow up once we have an official announcement, so stay tuned and be the first to know!