Original Left 4 Dead DLC to hit "a month or so" after L4D2's The Passing

Valve has revealed during X10 that some DLC is heading to the original Left 4 Dead, in order to help explain how the original survivors came to be included in The Passing for Left 4 Dead 2.

According to Chet Faliszek, Left 4 Dead 2's survivors will meet up with the original group to help 'em finish the third map in the campaign.

It will also add a new uncommon infected to the mix called the Fallen Survivor, which are humans who wrongly though themselves to be immune to the infection. Sometimes, the Fallen will drop health and ammo when killed.

The Passing is slated for late March, and Valve plans to release the as-yet-unnamed L4D1 DLC a "month or so" later, and it will only be playable with the original game - until mods get hold of it, we reckon.

There are some new screens for The Passing up on Kotaku.