Some casting shake-ups on Clint Eastwood’s J. Edgar Hoover biopic J. Edgar today: Ed Westwick (Gossip Girl) officially joins the cast, while Charlize Theron opts not to take on the role of Hoover’s secretary. Westwick is set to play a clean cut operative who, after being assigned to write Hoover’s biography, begins to dig a little too deep into the enigmatic FBI director’s life. A few days ago, we told you that Armie Hammer (The Social Network) had signed on to star as Hoover’s lover and confidant Clyde Tolson opposite Leonardo Dicaprio as Hoover himself. Damon Herriman (FX’s Justified) and Dame Judi Dench round out the cast announced thus far, with Dench portraying Hoover’s mother. Deadline reports that Eastwood is now looking to cast either Amy Adams or Naomi Watts in the role of Hoover’s secretary.Vulture reports that Theron, who was never officially attached to the film, has ultimately decided not to take part in the film. Instead, the actress has signed on to star in Rupert Sanders’ Snow White and the Huntsman, and may be mulling over Ridley Scott’s Alien prequel. More after the jump.In addition to reporting Westwick’s addition to the cast of J. Edgar, Deadline also says Theron has officially signed on for Snow White and the Huntsman. Back in October, we told you that she was eying the role of the evil queen in the film Now it appears she’s decided to star in the film after-all. With little movement on the flick as of late (other than more casting rumors), this could mean that production is gearing to start up soon.Now on to that Alien rumor: While there’s no official word on this, and casting rumors regarding the Alien prequel have run rampant the past few months (not to mention highly inaccurately), Vulture is reporting that Theron will “get the new version of the Alien script sometime this week and make her decision soon.” They claim that Fox execs are keen on grabbing a big name star for the project, while Scott is partial towards Noomi Rapace (The Girl with the Dragon Tattoo). Apparently, if Scott casts Rapace as the star, the studio wants a big name actress to take on the supporting role of "Vickers." This supporting role is apparently being expanded, and that's the role that Theron is looking towards when she reads the script. Take this with a grain of salt, as there’s been little official news on the project as of late other than the denial of all previous casting rumors/supposed plot details.Theron is currently filming director Jason Reitman’s Young Adult, from a script by Diablo Cody (Juno). The film stars Patrick Wilson and Patton Oswalt and is set to be released sometime this year.