Guy d'Hardelot (August 1858 – January 7, 1936) was the pen name of Helen Rhodes (nee Helen Guy), a French composer, pianist, and teacher.
D'Hardelot was born as Helen Guy, to an English father and a French mother. She was born at Chateau d'Hardelot, near Boulogne-sur-Mer. This old castle, from which she took her pen name, was once occupied by Henry VIII and Anne Boleyn.
At the age of fifteen she went to Paris, where she studied at the Conservatoire de Paris under Renaud Maury and came under the notice of Charles Gounod and Victor Maurel, who were much impressed with her ability. She also met Jules Massenet, who encouraged her to compose. On coming to London she became a pupil of Clarence Lucas. Emma Calvé was a good friend to d'Hardelot, and did much to bring her songs into notice.
Most of her life, d'Hardelot was engaged in teaching singing and diction at her home in London, and many of her pupils attained success. In 1896 she toured the United States with Calvé. Her first real success as a composer was won with "Because", though her song "Sans Toi" had previously been favorably received. Among her other successes may be mentioned "I Know a Lovely Garden", "I Think", "I Hid My Love", "Dawn", and "A Bunch of Violets".