Update: Valve's Doug Lombardi has told Eurogamer that the game's due for PC and Xbox 360.
Original story: Valve has officially announced Portal 2.
The game is due out this "holiday season" ("Christmas" in old money) according to the developer.
Platforms were not mentioned.
The first Portal came out on PC, PS3 and Xbox 360 as part of The Orange Box, and then came to Xbox Live Arcade in the form of Portal: Still Alive.
Check out our Portal review for a reminder of what made it so lovely.
Valve has been hinting at Portal 2 for a while, even updating the original game's end sequence in a patch.