he British actor - best known for his role in 'Gossip Girl' - will star alongside Leonardo DiCaprio in the biopic movie about the Federal Bureau of Investigation's (FBI) chief J. Edgar Hoover.

He will be playing an operative with a special writing skill, who is discovered by Hoover and conscripted to write his biography.

Clint Eastwood is directing the movie, which is set to begin shooting in February at the latest.

Meanwhile, Charlize Theron - who was set for the role of civil servant Helen Gandy, Hoover's secretary - has pulled out of the project to take part in 'Snow White and the Huntsman'.

To replace her, Eastwood is considering both Naomi Watts and Amy Adams.

The movie was previously believed to be named 'Hoover' but has since been renamed 'J. Edgar', and will be produced by Brian Grazer and Rob Lorenz.

It has been written by 'Milk' scriptwriter Dustin Lance Black.