[UPDATE 3: Believe it or not, there's more. Gamescom organizers told Joystiq this: "We can not officially announce it. Please check our list for further changes. Please see the legend for information about the sources."
At this point, all I know is this: over the next couple of days, I will definitely be keeping an open mind, as well as my ears open.]
[UPDATE 2: Valve has stated to CVG that they will not be showing any games at Cologne this year, and the Half-Life 3 listing has been removed from the PDF document in question.]
[UPDATE: I have made a second call to the Gamescom public info line. I was explicitly informed by one of the managers, that Valve were the ones who asked that HL3 be placed on the list; but that apparently, "just a few minutes ago", Valve requested that HL3 be removed from that list.
Meanwhile, Eurogamer reports that they were notified by Gamescom representatives, that HL3 and Dragon Age 3 appearing on the listing was "a mistake". Gamescom reps denied comment on how and why the mistake was made, which is pretty strange.
The situation is murky, but it is still developing; don't get your hopes up just yet.]
Yes, this truly is the month when everything happened. Read on to find out how deep the rabbit hole really goes.