Game of Thrones producer David Benioff (who also wrote the screenplay for X-Men Origins: Wolverine) put the cart before the horse when he told an audience at the "Evening With Game of Thrones" event at the Academy of Television Arts and Sciences that George R.R. Martin, who wrote the series of epic fantasy novels upon which the TV series is based, would have a cameo in the hugely popular HBO TV show.
Turns out that Martin’s cameo won’t be in Game of Thrones Season 3, which kicks off March 31st, and which has already been shot. As Deadline reports today, Martin’s cameo appearance is contingent on HBO ordering a fourth season of Game of Thrones, an event that is highly likely given the enormous ratings that the first three seasons of GOT has piled up. Understandably HBO wants to see what happens when Season Three debuts, before committing to another season, but frankly a fourth season pick-up is pretty much the definition of a "foregone conclusion."
Martin actually filmed a cameo that was to have been included in the original Game of Thrones pilot, but the pilot was almost completely re-shot and Martin’s appearance landed on the cutting room floor. The inclusion of a Martin cameo makes sense, especially given the fact that the author recently signed an expanded deal with HBO to develop and produce new series for the pay cable network (see "George R.R. Martin Expands HBO Deal").