Here is the announcement, via The Pokemon Company:
A new Pokemon mobile game called Pokemon Masters is on the way for iOS and Android devices from The Pokemon Company and DeNA. Pokemon Masters enables players to experience a new type of Pokemon battling on the go and features many famous Pokemon Trainers from the long history of Pokemon video games. Gameplay will be optimized for smart devices for a casual but uniquely Pokemon experience. Fans can expect more details about Pokemon Masters in June.