EXCLUSIVE: Naomi Watts has signed on to star in J. Edgar, the Clint Eastwood-directed biopic. Watts will play Helen Gandy, J. Edgar Hoover’s loyal secretary for 54 years. Hoover (played by Leonardo DiCaprio) called her indispensible and she was the ultimate keeper of his secrets and a behind the scenes influence on the workings of the FBI. After Hoover died, Gandy spent weeks destroying his personal file, which contained the incriminating material that he used to manipulate and control the most powerful figures in D.C.  Imagine’s Brian Grazer is producing with Eastwood and his Malpaso partner Rob Lorenz.

Watts takes the role that Charlize Theron was once expected to play, before she moved on to play the Evil Queen in Snow White and the Huntsman and to likely be in the cast of the Ridley Scott-directed Prometheus. Watts had been the frontrunner, but the studio considered other actresses because it looked like her schedule wouldn’t work out. It has.

Aside from DiCaprio and Watts, Ed Westwick is set to play Agent Smith, a clean-cut operative hired by Hoover to write his biography; Josh Lucas plays aviator Charles Lindbergh; Damon Herriman plays Bruno Hauptmann, the German immigrant accused of kidnapping Lindbergh’s 20-month baby in 1932. Called the crime of the century, Hauptmann’s trial was a major case for Hoover;  Ken Howard is playing U.S. attorney General Harlan F. Stone and Armie Hammer is set to play Clyde Tolson, Hoover’s alleged lover. Erica Huggins is exec producer.

Watts most recently wrapped The Impossible and Dream House. She’s repped by CAA and Untitled.