Question: Which German-American pianist, conductor, and composer wrote the score for Katharine Hepburn's only stage musical? 

Context articles: Katharine Houghton
André Previn
Guess Who's Coming to Dinner
Emil Liebling
Katharine Martha Houghton Hepburn
Katharine Hepburn performances
Heinrich Gebhard
Coco (musical)
Morning Glory (1933 film)
The Katharine Hepburn Cultural Arts Center

Katharine Houghton (born Katharine Houghton Grant; March 10, 1945) is an American actress and playwright.
 She portrayed Joanna "Joey" Drayton, a white American woman who brings home her black American fiancé to meet her parents, in the 1967 film "Guess Who's Coming to Dinner".
 Katharine Hepburn, who played the mother of Houghton's character in the film was, in real life, Houghton's aunt.
André George Previn, KBE ( ; born Andreas Ludwig Priwin; April 6, 1929) is a German-American pianist, conductor, and composer.
 Previn is the winner of four Academy Awards for his film work and ten Grammy Awards for his recordings (and one more for his Lifetime Achievement).
Guess Who's Coming to Dinner is a 1967 American comedy-drama film produced and directed by Stanley Kramer, and written by William Rose.
 It stars Spencer Tracy, Sidney Poitier, and Katharine Hepburn, and features Hepburn's niece Katharine Houghton.
 The film contains a (then rare) positive representation of the controversial subject of interracial marriage, which historically had been illegal in most states of the United States, and still was illegal in 17 states—mostly Southern states—until 12 June 1967, six months before the film was released, roughly two weeks after Tracy filmed his final scene (and two days after his death), when anti-miscegenation laws were struck down by the Supreme Court in "Loving v. Virginia".
 The film's Oscar-nominated score was composed by Frank De Vol.
Emil Liebling (April 12, 1851 – January 20, 1914) was a German-American pianist and composer.
Katharine Martha Houghton Hepburn (February 2, 1878 – March 17, 1951) was an American feminist social reformer and a leader of the suffrage movement in the United States.
 Hepburn served as president of the Connecticut Woman Suffrage Association before joining the National Woman's Party.
 Alongside Margaret Sanger, Hepburn co-founded the organization that would become Planned Parenthood.
 She was the mother of Academy Award winning actress Katharine Hepburn.
Katharine Hepburn (May 12, 1907 – June 29, 2003) was a major American actress of the 20th century who appeared in 44 feature films, eight television movies and 33 plays for over 66 years.
 Hepburn began her career in theatre in the late 1920s, and later appeared on the stage in every decade up until the 1980s.
 Productions Hepburn played in ranged from Shakespeare, to Philip Barry comedies, work by George Bernard Shaw, and a musical.
 Hepburn made her film debut in "A Bill of Divorcement" in 1932.
 Over the next six decades, she appeared in a range of genres, including screwball comedies, period dramas, and adaptations of works by notable playwrights Tennessee Williams, Eugene O'Neill, and Edward Albee.
 Her final appearance in a theatrically released film was a supporting role in "Love Affair" in 1994.
 Hepburn first appeared in a television movie in 1973, and later continued to appear in the medium until she gave the final performance of her career in "One Christmas" in 1994.
 Hepburn also presented two documentaries for television, and narrated two short documentaries.
Heinrich Gebhard (July 25, 1878 in Sobernheim, Rhineland-Palatinate, Germany – May 5, 1963 in North Arlington, New Jersey, United States) was a German-American pianist, composer and piano teacher.
Coco was a 1969 Broadway musical with a book and lyrics by Alan Jay Lerner and music by André Previn, inspired by the life of Coco Chanel.
 It starred Katharine Hepburn in her only stage musical.
Morning Glory is a 1933 Pre-Code American drama film which tells the story of an eager would-be actress and her journey to stardom, and what she loses as a result.
 The picture stars Katharine Hepburn, Douglas Fairbanks, Jr., and Adolphe Menjou, was adapted by Howard J. Green from a then not yet stage produced play with the same name by Zoë Akins, and was directed by Lowell Sherman.
 Hepburn won her first Academy Award for Best Actress for this movie.
 "Morning Glory" was remade in 1958 under the title "Stage Struck".
The Katharine Hepburn Cultural Arts Center is a theater in Old Saybrook, Connecticut that opened in 2009.
 It is the only theater in the world that is named for Katharine Hepburn, the 4-time Academy Award winning actress.