According to Katie McGrath’s profile she has been cast in the upcoming movie from director Guy Ritchie. Katie’s mentioned also on the ImDB to portray a character named Elsa. Knights of the Roundtable: King Arthur is an upcoming epic adventure film directed by Guy Ritchie and written by Joby Harold. The film stars Charlie Hunnam as Arthur. It is scheduled for a July 22, 2016 release.

Source