Next Week's White Dwarf reveals Nagash, along with a good picture of his rules and items. He is looking to be a beast, wielding his staff of power, his books of Nagash, Mortis Blade, and Black Armour.
The leaks can be seen in many places, and first appear on the El Taller de Yila, and picked up by Talk Wargaming.
Spanish
http://eltallerdeyila.blogspot.com.es/2014/08/reglas-nagash-el-rey-viene-para-quedarse.html?m=1
English
http://www.talkwargaming.com/2014/08/leaks-leaked-white-dwarf-image-of-nagash.html