Creative Assembly has long been hyping up a giant reveal for the Game Developers Conference (GDC), and it turns out their grand anouncement was for a game known as Total War: Arena.
Total War: Arena is a free-to-play online game with a Multiplayer Online Battle Arena (MOBA) style of gameplay, in which history's greatest commanders are pitched against one another in a spectacular team-based battle. Arena will consist entirely of online play, and combines Real Time Strategy with MOBA play. The game is being developed at Creative Assembly's UK brach.
There is currently a closed beta which you can register for.