Valve has announced that if you pre-order Left 4 Dead 2 on PC you will gain access to Bill's hat in Team Fortress 2.
"For the first time in history, two separate Valve universes collide. That's right: it's a Left 4 Dead/Team Fortress crossover!" screams the official website. "This is not fan fiction! This is not a dream sequence! The characters from Team Fortress 2 will team up with Bill's hat from Left 4 Dead 1!
"And lest you think this is just some marketing gimmick, here's the intricate back-story justifying it: while conducting a science experiment on parallel dimensions, Bill's hat fell off a table into the Team Fortress universe."
Genius. As you can see from the image on the blog, the hat looks great whoever you play. "Is Bill's hat the tenth class? All will be revealed in time, but don't hold your breath."
In the meantime, if you pre-order - or have already - then next time you load up Team Fortress 2 you will have use of the hat.
Left 4 Dead 2 is due out for PC and Xbox 360 on 20th November (17th on Steam), and was proving popular at the Eurogamer Expo last week, where Valve's Chet Faliszek presented it live and presided over showfloor gameplay too. What a guy.