Have you given up on ever seeing Half Life 2: Episode 3 yet? No? Well good, because you're about to see something that's going restore your unhealthy conspiratorial streak.
If the guys at ValveTime are to be believed, the following images are concept art from the long-awaited third episode of Half-Life 2. The images are from 2008, indicating that Valve may have been working on Episode 3, but eventually put the project on indefinite hold.
The images includes some potential information on the story of the presumed-defunct game - some of the images Alyx wearing her father's clothes. Make sure to incorporate that information in your Half-Life 3 fan-fiction/script/conspiracy blog.