Heath Ledger's diary reveals Joker prep for the film The Dark Knight Heath Ledger included this photograph of himself in Joker makeup in the diary he kept while researching the role. The diary was revealed in a new documentary Too Young to Die. HEATH Ledger's diary reveals he "immersed" himself in his final role as the Joker, according to his father. The late actor's diary has been revealed for the first time, showing a performer who was devoted to his craft while preparing for his dramatic role in The Dark Knight. Kim Ledger shared the diary as part of a German documentary called Too Young to Die. The film shows Mr Ledger opening a red and blue bound book, containing notes, drawings, photos of clowns and other images from comic books. The actor also appears to have been inspired by Malcolm McDowell's character in A Clockwork Orange, as he has included an image in the diary. "This is the diary," Mr Ledger says in the clip posted to Reddit Thursday evening. Heath Ledger scrawled this message in the diary he kept while researching the Joker role. As Mr Ledger nears the end of the book there is a picture of his son in the Joker costume and makeup. He scrawled over the photo in silver marker. This is a make-up test which was done eight months before. Before the end of the shooting he wrote 'bye bye' on the back of the page," his father said. It was hard to see this. Ledger was 28 when he was found dead in his New York home in January 2008. He posthumously won the Best Supporting Actor Oscar for his role in The Dark Knight.