Peter Jackson announced that he would direct the sequel once he had finished "The Hobbit" trilogy. Two years before "The Secret of the Unicorn", Jackson mentioned that his favorite "Tintin" stories were "The Seven Crystal Balls", "Prisoners of the Sun", "The Black Island", and "The Calculus Affair", but he had not yet decided which stories would form the basis of the second film. He added "it would be great" to use "Destination Moon" and "Explorers on the Moon" for a third or fourth film in the series.