I hear Marvel has been somewhat coy about its one-word "King" announcement at last summer's San Diego Con. I'm not sure why this is a good idea beyond extending the number of speculative articles; if it ends up being something other than "Stephen King will write something for us," I can't see how the original teaser could be viewed as anything other than a display of contempt for the kind of fans who follow those things. Anyway, this article seems to say that the popular author writing for the company is exactly what Marvel meant. The more interesting part is the statement that the graphic novel would also serve as the next book in King's current Dark Tower fantasy series.
Update: E-mail tells me it's a prequel, which is slightly less interesting. And apparently, Publisher's Weeklyconfirms.