According to Dutch site PS3Hype, there was a small gaming event in Amsterdam, where they met with game studio developers in the Netherlands.
During this event, one of the developers from Guerrilla Games (Killzone 2) mentioned Killzone 3.
Then the http://www.gamekings.tv/index/videos/brievenmaandag-9/ (link now dead) asked someone close to Guerrilla Games about the co-op patch for Killzone 2 and this is what he said, to quote:
"They [Guerrilla Games] are really kicking themselves because of that. They have a handful of developers working on updates, and patches for Killzone 2, but I doubt we´ll see co-op patch.
The problem is the seamless loading. Cross console synching seems to be an issue - but from what I gather the key developers of Killzone 2 are working on a new project."
They asked him if he was referring to Killzone 3, and he said:
"Ahh, well - I can´t say for sure, but it seems very likely. They have a team working on writing up algorithms, and modifying the Killzone 2 engine, and a select few working on a story. It hasn't been confirmed but for now, we suspect that Guerrilla Games is indeed working on Killzone 3."
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