Game Informer has revealed that Portal 2 is in development at Valve, with the title described by the publication as a "full-fledged, standalone sequel".

The first title was originally sold as part of the excellent Orange Box (Half-Life 2, Ep1, Ep2, Team Fortress 2 and Portal) and was also sold on its own via Steam. An updated version was also released as a standalone download on XBLA.

The upcoming issue of Game Informer has a 12-page preview, promising details on new gameplay mechanics, storyline and some surprising twists. The cover art for the magazine also suggests the action will take place both inside the Aperture Science Enrichment Center and outside.

We can't wait.

Valve's announced Portal 2 will ship this holiday season. No platforms have been confirmed.