Robert Carradine, the US actor best known for roles in Revenge of the Nerds and Lizzie McGuire, has died aged 71. In a statement, his family said the actor took his own life after living with bipolar disorder for nearly two decades. The Carradine family said they wanted to announce his cause of death to raise awareness of "the stigma that attaches to mental illness". "We want people to know it, and there is no shame in it," his brother Keith told Deadline. Lizzie McGuire star Hilary Duff led the tributes to her former on-screen father, writing on Instagram: "This one hurts. It's really hard to face this reality about an old friend." Born on 24 March 1954, Carradine was the youngest son of John Carradine and a brother of actors David and Keith Carradine. Encouraged by his brother David, Robert Carradine auditioned for 1972's The Cowboys, a John Wayne film that became his first screen role.…