You might want to work on your remembering, because on the "site with dates", they announced a hero reveal for April 25th. Here, check the link:
http://us.battle.net/heroes/en/heroes20/
New Hero:Details unlock April 25
Cassia and Genji are already shown as unlocked, so it's not them. Female Diablo is not a new hero, so it's not her, either. She may well appear in the cinematic, but she is NOT the new hero being teased.