Frederick Lonsdale was a British playwright known for his librettos to several successful musicals early in the 20th century, including King of Cadonia (1908), The Balkan Princess (1910), Betty (1915), The Maid of the Mountains (1917), Monsieur Beaucaire (1919) and Madame Pompadour (1923). He also wrote comedy plays, including The Last of Mrs. Cheyney (1925) and On Approval (1927) and the murder melodrama But for the Grace of God (1946). Some of his plays and musicals were made into films, and he also wrote a few screenplays.

The Balkan Princess is a musical in three acts by Frederick Lonsdale and Frank Curzon, with lyrics by Paul Rubens and Arthur Wimperis, and music by Paul Rubens. It opened at London's Prince of Wales Theatre on 19 February 1910. The cast included Isabel Jay and Bertram Wallis. There was a successful Broadway run in 1911 that used a libretto by Leonard Liebling, and the show toured widely thereafter.