Update: And here's yer trailer. CD Projekt has confirmed the arrival of Gwent on-stage, and the beta will arrive in September.
Original: The rumors are true: a standalone Gwent card game is on the way. This news comes not from E3—although I'm expecting it—but the official Play Gwent site that's already live. More importantly, it's already taking beta sign-ups.
Witcher 3 players ought to be familiar with the rules, but there's a interesting twist: an open, event-based world. "To be released in episodes, the story unfolding in the campaign will feature the choice and consequence mechanic the Witcher games are known for."
If you're not a Witcher 3 player or you skipped out on all the Gwent, there's already a short tutorial on the site.
There's a trailer, currently set to private. We'll update you as soon as it goes live.