Killzone: Shadow Fall was a launch title for Playstation 4, but despite that and the fact that Horizon: Zero Dawn was announced at E3 only two months ago, the latter was actually in development before Shadow Fall.
This was revealed by Guerrillas co-founder Hermen Hulst in the latest issue of Official Playstation Magazine, where he says:
"We actually commenced on the Horizon Zero Dawn project before we commenced on Killzone Shadow Fall. So I was going to say it's been a huge benefit that we started with a mature engine, but the mature engine came into existence whilst the development of Horizon was ongoing! But nevertheless, because we were working on Shadow Fall, of course, to obviously have an engine ready at launch of PlayStation 4 was a boon to us."
Horizon: Zero Dawn will be launched next year, exclusively on Playstation 4.
Thanks GamesRadar