We normally don't post "an announcement about an announcement," but the way this one is being hyped up, it seems like it'll be something you don't want to miss. Games Workshop will be making big 40k announcements and previews this upcoming Saturday on their Twitch channel.
From the article:
This week will end with a bang heard around the galaxy, as we blow the lid off something huge for the 41st Millennium. There’s so much Warhammer 40,000 goodness packed into this preview that we couldn’t fit anything else in…
Catch it on Saturday, May 23rd, live on Twitch from 1:45 pm UK time. As always, we’ll round up the news as it breaks in a massive article in case you’re not able to catch it live. We’ll have more info for you as we get closer, but let’s just say you might want to clear your calendar and arrange an online watch party with your friends for this one.