Worlds are colliding! Valve’s Left 4 Dead blog announced the impending release of the crossover DLC The Passing, which joins up the casts of both Left 4 Dead and Left 4 Dead 2:

…if it was coming out next week we would say right here – Left 4 Dead 2’s The Passing is coming out next week and we will be updating the blog next week with more news on the release. There you go.

For those wondering whether or not we’ll be seeing zombified versions of the Left 4 Dead characters, a slightly spoilerish video from Gametrailers hints that we might not want to get too attached to our heroes…

Additionally, fans of Left 4 Dead 2’s Dark Carnival campaign should check out Rock Band’s new offerings this week. A pair of songs from Midnight Riders, the game’s fictitious state fair rockers, are both up for download. Sky flowers sold separately.

The Passing arrives later this week with a 560 MS point price tag.