Question: Loudon Wainwright III is related to which American independent folk singer?
Context: Loudon Snowden Wainwright III (born September 5, 1946) is an American songwriter, folk singer, humorist, and actor.  He is the father of musicians Rufus Wainwright, Martha Wainwright, and Lucy Wainwright Roche; brother of Sloan Wainwright; and former husband of the late folksinger Kate McGarrigle.  He resides in Canada. Album III, as its title indicates, is the third full album from Loudon Wainwright III.  It was originally released in 1972 on Columbia Records.  "Album III" would spawn Loudon Wainwright's most popular hit single, "Dead Skunk", one of the many 'novelty songs' sprinkled throughout Wainwright's career.  Although Wainwright has maintained an ironic, sometimes sepulchral sense of humor, "Dead Skunk", despite its commercial success, has dogged him ever since, as he comments on 1985's album "I'm Alright", "Were you embarrassed about 'Dead Skunk'"? History is the twelfth studio album by American singer-songwriter Loudon Wainwright III, released on September 21, 1992 on Charisma Records.  The album was recorded following the death of Wainwright's father, Loudon Wainwright Jr..  Regarding his father's death and its influence on "History", Wainwright stated that: Lucy is the debut studio album by American folk musician Lucy Wainwright Roche, released on October 26, 2010 on Strike Back Records.  Produced by Stewart Lerman, the album features appearances from Roche's father Loudon Wainwright III, The Roches, Steuart Smith, David Mansfield and Kelly Hogan. Loudon Snowden Wainwright Jr. (December 16, 1924 – December 12, 1988) was an American writer.  He was the father of folk singer Loudon Wainwright III and singer Sloan Wainwright, and grandfather to Rufus Wainwright, Martha Wainwright, and Lucy Wainwright Roche. Martha Wainwright (born May 8, 1976) is a Canadian-American folk-rock singer-songwriter.  She is the daughter of American folk singer and actor Loudon Wainwright III and Canadian folk singer-songwriter Kate McGarrigle.  She was raised in a musical family along with her older brother, Rufus Wainwright, in Montreal, Quebec, Canada. Sloan Wainwright (born 1957) is an artist and member of the American independent music scene.  Her musical style consists of a combination of folk, rock, jazz, and blues, an approach which owes itself to her time writing and performing throughout Greenwich Village. Recovery is the nineteenth studio album by American singer-songwriter Loudon Wainwright III, released on August 19, 2008 on Yep Roc Records.  The songs are "re-covers" from his first four albums: "Loudon Wainwright III" (1970), "Album II" (1971), "Album III" (1972) and "Attempted Mustache" (1973). Songs in the Dark is the debut album by the Wainwright Sisters, a singer-songwriter duo featuring the Canadian-American Martha Wainwright and her American half-sister Lucy Wainwright Roche.  The album, released on November 13, 2015, includes lullabies that their mothers Kate McGarrigle and Suzzy Roche sang to them as children, plus songs by Woody Guthrie, Jimmie Rogers, and their father Loudon Wainwright III. Loudon Wainwright III (also known as Album I) is the debut album of Loudon Wainwright III.  It was released on vinyl in 1970 on Atlantic Records.  Like his second effort "Album II", the album is a solo acoustic effort.  Though his ironic sense of humour is evident, this is an altogether bleaker and more acerbic album ("Black Uncle Remus", "Four is a Magic Number", "Glad To See You've Got Religion") than most of his 1970s work.
Answer: Sloan Wainwright