At Microsoft's E3 2011 keynote today at the Galen Center, Halo 4 was officially announced -- surprise! Master Chief and Cortana are back (kicking off a new trilogy, apparently), the brief teaser trailer showed. 343 Industries is at the reigns with a Holiday 2012 launch date proposed.

Update: Hit the jump for the teaser!

This article was originally published on Joystiq.