Directly to you from Twitter:
Get your Heroes ready for the next Grand Hero Battle starting 3/24 as the Ambitious King, Michalis is coming!… twitter.com/i/web/status/8…—
Nintendo of America (@NintendoAmerica) March 15, 2017
…Wanna play? Buy a 3DS.
That being said, click on Fire Emblem Heroes for everything you need to know about the game. 😀