Helena will portray her real-life step-great-grandmother in World War I drama, The Guns of August
, according to Variety
. Helena will play Margot Asquith
in the film, based on Barbara W. Tuchman’s book of the same name. Charles Dance
will play Helena’s great-grandfather, Liberal Prime Minister Herbert Henry Asquith, while Emilia Clarke
will play her grandmother, Violet. Oliver Hirschbiegel
will direct, and Frank Doelger
will write the script.