Source: MTV Friday, September 10, 2004
George Lucas talked to MTV and he reassured that Star Wars: Episode III - Revenge of the Sith is the last live-action film in the saga (though a TV series is in the works, more on that here).
"The original 'Star Wars' was only three films, and that was what it was meant to be," Lucas said. "After a lot of pondering and thought, I went back to do the back story, but that pretty much tells the story. Episode six is the end. There isn't any more to it."
THE HISTORY ACCORDING TO GEORGE:
THE STORY CHANGES EVERYTIME HE TELLS IT, WHEN MY GRANDMA STARTED DOING THIS WE PUT HER IN AN OLD FOLKS HOME.