Robert Downey Jr has offered to help Keith Urban deal with his demons.

A former rehab patient himself, Downey Jr has reportedly offered his help to Urban and his wife Nicole Kidman after he heard that the country singer was suffering a relapse in his battle with alcoholism.

Robert Downey Jr plans to reveal all in his autobiography.

The "Kiss Kiss Bang Bang" star signed a book deal with Harper Entertainment on Thursday and has promised readers a "candid look at the highs and lows of his life and career".