Juno Temple and Alexandra Roach are to play Princesses Margaret and Elizabeth on the big screen.
The British actresses will portray the royal sisters as teenagers in Girls' Night Out, with Dark Knight Rises star Juno as Margaret and The Iron Lady's Alexandra as Elizabeth, reports Screen Daily.
It was previously reported that Twilight actress Dakota Fanning was attached to play Princess Margaret, but it seems the role has gone to Juno.
Inspired by real events, the film is set on V.E. day in 1945 and sees the young princesses allowed to leave Buckingham Palace for the night to join in the celebrations outside.
The film was penned by Trevor De Silva and will be directed by Michael Hoffman, who was at the helm of award-winning biographical drama The Last Station.
Ecosse Films' Robert Bernstein said he was "delighted to be working with such exciting British talent".
Girls' Night Out begins shooting in the UK later this year.