Killzone 4 in "early concept development"

When we broke the news about the MGS HD bundle being released before any other sites, it caused a slight uproar.
Well, here's for another.
One of our sources has confirmed that Guerrilla Games has just started work, mainly concept ideas, for Killzone 4 but the game won't be officially announced until E3 next year, when Sony will possibly reveal details about its PlayStation 4 console.

Our source said, "The guys at Guerrilla were given a break after the Killzone 3 development, some time to refresh, and work on Killzone 3 patches and content, but also to get a much needed breather.  I just spoke with one of the guys on the development team, and he confirmed that Killzone 4 has now entered early concept development, but Sony's giving them a lot of time with this one, apparently not planning on anything "official" to announce/show until next year's E3."

Hopefully whatever ideas the guys had already thought of, work out well for the next game in the series!