So, just looked on the GW website and yeah, see for yourself (you'll need a GW account to see the full thing) [url]https://www.games-workshop.com/gws/content/article.jsp?catId=&pageMode=multi&categoryId=§ ion=&pIndex=0&aId=14300088a&start=1[/url]
If you don't have an account it still comes up saying an April release, but for those of you who want a bit more, I've copied some of the stuff:
"This April Games Workshop releases Codex: Grey Knights, alongside a comprehensive range of fantastically detailed Citadel miniatures. Although details are being kept firmly under wraps for now, you can expect an exciting selection of plastic kits to enable you to build your own Grey Knights army."
As usual they've said about putting updates about it on their 'What's new today!' blog and bits in White Dwarf, so there we have it, Grey Knights!