Ralph Fiennes, Hayley Atwell and Dominic Cooper have joined the cast of Saul Dibb's "The Duchess" reports Variety.

Based on Amanda Foreman's biography of the scandalous 18th century English aristo Georgiana, Duchess of Devonshire, the movie is being co-financed by Pathe and BBC Films.

Keira Knightley has already been cast as Georgiana, Fiennes will play her husband, the Duke of Devonshire, with Cooper as her lover Earl Grey and Atwell as her best friend, Lady Bess Foster.

Shooting begins September 23rd in London.