Princess Knight, by Tezuka Osamu, is being published by Vertical.
To say that this is a "long-awaited" announcement is sort of an understatement. Start saving your money now, seriously, because I expect everyone who calls themselves a Yuri fan to run out and get this. No exceptions, no excuses. If you can afford a pizza, you can afford this book. (If you really can't afford this book, ask your library, nicely.)
Princess Knight, aka Ribon no Kishi （リボンの騎士）is one of the seminal works of Yuri fandom. Tezuka's visible influences include Disney's Snow White and Takarazuka, and this series set the bar for notable later girl-princes such as Lady Oscar in Rose of Versailles and Tenjou Utena in Revolutionary Girl Utena.
If you have been paying the least bit of attention to the manga and Japanese lit worlds, Vertical's other two announcements will be pretty big news, as well. So this was a great off-season announcement for all of us.