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You read it right, the November issue of PC Gamer indeed has a first look at the last episode in the trilogy. Besides advertising a first artwork of the game, it also hints at its new setting, a lost cargo ship called Borealis.
You may glance at a scan of this sneak look on this website.
Beware though, it reveals some information on the ending of Episode Two!
It is in French, so here is my go at translating:
The November issue of PC Gamer magazine confirms the development of half-life 2: Episode Three and we bring some information on the scenario of this new opus (small Attention spoiler of half-life end 2: Episode Two). In half-life end 2: Episode Two, Gordon and Alyx look at a video recorded by Judith Mossman, a scientist that works along side Eli Vance and resistance. Mossman retrieves the discovery of a lost freighter, the Borealis, which is supposed to transport a new technology developed by a mysterious laboratory, better known under the Aperture name Science and big rival of Black Mesa.