Consequently , Arthur returns to Britain and fights Modredus at the fatal Battle of Camlann .
While her husband is absent , Guinevere is seduced by Modredus and marries him , and Modredus declares himself king and takes Arthur 's throne .
Arthur returns to Britain and fights Modredus at the fatal Battle of Camlann .
While her husband is absent , Guinevere is seduced by Modredus and marries him , and Modredus declares himself king and takes Arthur 's throne .