Robert Downey, Jr. has returned the advance on his memoirs after postponing plans for a tell-all. The actor had signed up to write about his life, his career and the drug problems that famously almost destroyed him - but now publishers at HarperCollins have been told the tome won't be written, according to the Associated Press. Downey Jr's spokeswoman Britney Ross has declined to go into details about the Iron Man star's decision. HarperCollins announced the project two years ago ; the book was due to hit shelves later this year .