Question: What British actor, producer, and socialite, who lived in the United States throughout his adult life starred in a 1948 American musical film starring Judy Garland?

Context articles: Peter Lawford
The Judy Garland Show
The Pirate (1948 film)
Presenting Lily Mars
The Harvey Girls (novel)
Easter Parade (film)
A Star Is Born (1976 film)
Babes on Broadway
A Star Is Born (1954 film)
The Clock (1945 film)

Peter Sydney Ernest Lawford (born Peter Sydney Ernest Aylen; 7 September 1923 – 24 December 1984) was a British actor, producer, and socialite, who lived in the United States throughout his adult life.
The Judy Garland Show was an American musical variety television series that aired on CBS on Sunday nights during the 1963-1964 television season.
 Despite a sometimes stormy relationship with Judy Garland, CBS had found success with several television specials featuring the star.
 Garland, who for years had been reluctant to commit to a weekly series, saw the show as her best chance to pull herself out of severe financial difficulties.
The Pirate is a 1948 American musical film produced by Metro-Goldwyn-Mayer.
 With songs by Cole Porter, it stars Judy Garland and Gene Kelly with co-stars Walter Slezak, Gladys Cooper, Reginald Owen, and George Zucco.
Presenting Lily Mars is a 1943 American musical film directed by Norman Taurog, produced by Joe Pasternak, starring Judy Garland and Van Heflin, and based on the novel by Booth Tarkington.
 The film is often cited as Garland's first film playing an adult type role (although "For Me and My Gal", released the previous year, is also often credited thus).
 Tommy Dorsey and Bob Crosby appear with their orchestras in this Metro-Goldwyn-Mayer production.
The Harvey Girls is a novel published in 1942 by Samuel Hopkins Adams.
 In 1946, it was adapted into an eponymous MGM musical film starring Judy Garland.
Easter Parade is a 1948 American musical film starring Judy Garland, Fred Astaire and Peter Lawford, featuring music by Irving Berlin, including some of Astaire and Garland's best-known songs, such as "Easter Parade", "Steppin' Out with My Baby", and "We're a Couple of Swells".
 The story bears certain similarities to Pygmalion.
A Star Is Born is a 1976 American musical drama film telling the story of a young woman, played by Barbra Streisand, who enters show business, and meets and falls in love with an established male star, played by Kris Kristofferson, only to find her career ascending while his goes into decline.
 It is a remake of two earlier versions – the 1937 version was a drama starring Janet Gaynor and Fredric March, and the 1954 version was a musical starring Judy Garland and James Mason.
 It will be remade for a third time in 2018 starring Stefani Germanotta and Bradley Cooper.
Babes on Broadway is a 1941 American musical film starring Mickey Rooney and Judy Garland and directed by Busby Berkeley, with Vincente Minnelli directing Garland's big solo numbers.
 The film, which features Fay Bainter and Virginia Weidler, was the third in the "Backyard Musical" series about kids who put on their own show, following "Babes in Arms" (1939) and "Strike Up the Band" (1940).
 Songs in the film include "Babes on Broadway" by Burton Lane (music) and E.Y. "Yip" Harburg (lyrics), and "How About You?
" by Lane with lyrics by Ralph Freed, the brother of producer Arthur Freed.
 The movie ends with a minstrel show performed by the main cast in blackface.
A Star Is Born is a 1954 American musical film written by Moss Hart, starring Judy Garland and James Mason, and directed by George Cukor.
The Clock (UK title Under the Clock) is a 1945 American romantic drama film starring Judy Garland and Robert Walker and directed by Garland's future husband, Vincente Minnelli.
 This was Garland's first dramatic role, as well as her first starring vehicle in which she did not sing.