Cymbeline (1982)

Cymbeline (Richard Johnson), the King of Britain, is angry that his daughter Imogen (Dame Helen Mirren) has chosen a poor (but worthy) man for her husband. So he banishes Posthumus (Michael Pennington), who goes to fight for Rome. Imogen (dressed as a boy) goes in search of her husband, who meanwhile has boasted to his pal Iachimo (Robert Lindsay) that Imogen would never betray him. And Iachimo's determined to prove him wrong.