User blog comment:Mesmermann/George R.R. Martin: "The TV series moving along behind me like a giant locomotive"/@comment-5014364-20120615135838

Good find. As said before, they've got enough material from the current books to provide through Season 6, what with cutting Book 3 into two seasons due to its large size.

That gives us four years.

And of course, he *has* already explained to the TV producers the general outline and broad brushtrokes of the ending.