Fmulder points us to fantasy artist Adrian Smith’s blog, where he posted two illustrations he created for the Book of Cain. The first shows an unnamed demon of extraordinary size, which may or may not represent something we’ll see in the game. The second shows Lilith, and as Festerfaust points out in comments, her headdress and shoulder armor looks strikingly similar to Diablo, as “he” looks in Diablo III. Compare to this shot, for instance.
So um… coincidence? The Adrian Smith artwork was inspired by recent artwork of Diablo? This Lilith illustration is years old and it actually inspired the look of D3’s Diablo? Or is there some plot/story relationship between Lilith and Diablo, this time around? I haven’t heard mention of Lilith as a character in the game, even in the spoiler threads, so it’s kind of a mystery all around. If you’ve got any more info or just want to guess, hit the comments.