Complex sentence: The hat's name derives from the stage adaptation of George du Maurier's 1894 novel "Trilby"; a hat of this style was worn in the first London production of the play, and promptly came to be called "a" Trilby "hat".
Split into simpler sentences: The hat's name derives from the stage adaptation of George du Maurier's 1894 novel "Trilby". A hat of this style was worn in the first London production of the play, and promptly came to be called "a" Trilby "hat".