This is big news. Epic Games announced two days ago that Fortnite would be coming to IOS for a beta release on March 12. Later in the year it would be coming to Android. This is a move by Epic Games to compete with PUBG which is currently on mobile testing in China. Mobile Fortnite will also support cross play with PC/Mac/PS4/Xbox/Mobile. You will be required to join a invite list which will go live the same time the game comes out on IOS. They will start off with a few players and throughout the coming months.
Here is a link to the site : https://www.epicgames.com/fortnite/en-US/news/mobile-announce