UPDATE: Niantic has said the event will now end on 24th July - 11 days later than originally planned, giving you more chances to catch the newly announced Pikachu.
ORIGINAL STORY: It seems like only yesterday tabloids were warning readers over a brand new mobile game, that police were telling people not to enter its police stations to catch virtual creatures or "Pokémon and drive", and an animal shelter used the app to find new volunteer dog-walkers, but here we are - the phenomenon that is Pokémon Go turns one year old today.
To celebrate its first anniversary, until 13th July all Pikachu found in the wild will wear Ash's famous hat from the Pokemon animated series.
It's not the first time Pikachu has seen a makeover in the game - the electric mouse donned a Santa Claus hat over Christmas, and a birthday hat to celebrate the franchise's own anniversary.
There will also be a new Anniversary Box store item for a limited time, featuring Incubators, Max Revives, Ultra Balls and a Raid Pass at a discount.
You can read more on how the event works and the best chances of catching your own Ash Hat Pikachu with our guide page.
There's more to come, too, with Niantic teasing Legendary Pokemon due this summer.
As a reminder of the frenzy of last summer, here's Chris, Johnny and Aoife taking to the streets of Brighton to see who can catch the rarest creature in 30 minutes: