Question: Bill Monroe's bluegrass song Blue Moon of Kentucky was released by Elvis Presley on the B-side of his first ever single. What was that song? 

Context articles: Unchained Melody: The Early Years
Moody Blue (song)
That's All Right
Lonesome Pine Fiddlers
Uncle Pen (song)
Blue Moon of Kentucky
Wooden Heart
Blue Moon (1934 song)
When My Blue Moon Turns to Gold Again
The Bluegrass Album (Alan Jackson album)

Unchained Melody: The Early Years or simply The Early Years is a compilation album by American country singer LeAnn Rimes, released in the United States on February 11, 1997 (see 1997 in music) by Curb Records.
 Due to high sales of her debut album, "Blue", the album consists of tracks recorded previously to "Blue" (tracks one, two and five through nine were taken from Rimes' independent album, under Nor Va Jak label, "All That" (1994). "
Unchained Melody" (originally by The Righteous Brothers) was released on a single as a B-side track with "Put a Little Holiday in Your Heart" at Target stores during the 1996 Christmas season alongside Rimes' debut album.
 The album contains cover versions of "I Want to Be a Cowboy's Sweetheart" by Patsy Montana, "Blue Moon of Kentucky" by Bill Monroe, "I Will Always Love You" by Dolly Parton, "Yesterday" by The Beatles.
 The album has been certified 2× Platinum for shipments of two million copies in the United States.
"Moody Blue" is a song made famous by Elvis Presley.
 The song was written by Mark James who also penned Elvis' "Suspicious Minds".
 "Moody Blue" was Presley's last No. 1 hit in his lifetime, topping the "Billboard magazine" Hot Country Singles chart in February 1977.
 "Moody Blue" also peaked at number thirty-one on the Hot 100.
 RCA Records also issued an extremely limited quantity of the "Moody Blue" single in an experimental translucent blue vinyl pressing, with "She Thinks I Still Care" as the B-side.
 Six months after "Moody Blue" topped the chart, Presley was dead.
"That's All Right" is a song written and originally performed by blues singer Arthur Crudup.
 It is best known as the first single recorded and released by Elvis Presley.
 Presley's version was recorded on July 5, 1954, and released on July 19, 1954 with "Blue Moon of Kentucky" as the B-side.
 It is #113 on the 2010 "Rolling Stone" magazine list of the "500 Greatest Songs of All Time".
The Lonesome Pine Fiddlers (1938- 1966) were an early bluegrass band which included such notable "first generation" bluegrass musicians as Ezra Cline, Bobby Osborne, Paul Williams, Melvin Goins, Charlie Cline, Curly Ray Cline, Larry Richardson and for a short time Jimmy Martin.
 The group was started by Ezra Cline and Curly Ray Cline and was originally named "Cousin Ezra and the Lonesome Pine Fiddlers".
 The Clines came from a large family consisting of musically talented people.
 Ray and Charlie's father, Charlie, was a talented banjo player and the women in the family, Geraldine and Bobbi, were great singers.
 For reasons unknown, Bobbi and Geraldine never joined the band on the road but often joined in at home, especially when notable Country singers, such as Bill Monroe, Lester Flatt and Earl Scruggs, and Hank Williams, came visiting.
 None of them ever had a music lesson yet excelled on every instrument they touched.
 Natives of the Gilbert Creek region of southern West Virginia, Cousin Ezra, along with brothers Ireland (Lazy Ned) and Curly Ray Cline, were part of the original Lonesome Pine Fiddlers from about 1938, a group that worked on radio at WHIS Bluefield, West Virginia.
 During World War II, Ned was killed in action.
 When the Pine Fiddlers resumed regular daily broadcasts, Charlie, who played multiple instruments, joined them on a regular basis.
 Charlie returned to the Fiddlers briefly before becoming a member of Bill Monroe's Blue Grass Boys.
 During 1952-1955, Charlie worked off and on with Monroe, recording some 38 songs, all on Decca.
 It has been said that he played every instrument at one time or another in the Monroe group except mandolin.
 Charlie spent most of 1953 back with the Lonesome Pine Fiddlers working at WJR radio in Detroit.
 When Ezra brought the band to Pikeville, Kentucky, in November, Charlie rejoined Bill Monroe.
 In 1954, Charlie did a session, playing lead guitar, with the Stanley Brothers and also another one on RCA with the Fiddlers, although he was not otherwise working with them at the time.
 He also worked briefly as a sideman with the Osborne Brothers, although he did not record with them.
 By 1958, Charlie (electric lead guitar) and his wife, Lee (electric bass), had rejoined Ezra and Curly Ray in the Lonesome Pine Fiddlers, who were experimenting with a more modern sound and working a TV show in Huntington, West Virginia, in addition to daily radio in Pikeville.
 In his later years, Charlie was with the Stanley Brothers.
 Curly Ray also played with the Stanley Brothers at a different time as their fiddler.
 Curly Ray was one of the best fiddlers in Bluegrass.
 This most talented family of musicians were the best, surpassed by none.
 Finally, on October 1, 2009, The Lonesome Pine Fiddlers got their due when they were inducted into the International Bluegrass Hall of Fame at the Ryman Theater (the original home of the Grand Ole Opry).
 Bobby Osborne, Melvin Goins and Paul Williams were there to receive the bands award.
 In the crowd of a sold out theater was the son of Ezra Cline, Scotty Ireland Cline, who recalled being in that same theater as a child sitting on stage and watching the Fiddlers play.
 (At the time, the Opry had bleachers for family just off stage).
 The final act of the evening at the IBMA Awards was the playing of "Pain in my Heart" by Osborne, Goins and Williams along with a Song from the Dillards, who were also inducted the same evening.
"Uncle Pen" is a song written and originally recorded by bluegrass legend Bill Monroe.
 Besides Monroe, the song was recorded by Porter Wagoner in 1956, Goose Creek Symphony in 1971, Michael Nesmith of "The Monkees" in 1973 on his solo album "Pretty Much Your Standard Ranch Stash," and Ricky Skaggs in 1984.
 "Uncle Pen" was Ricky Skaggs' ninth number one single on the country chart.
 The single went to number one for one week and spent a total of thirteen weeks on the country chart.
 Bill Monroe played a character named "Uncle Pen" disappointed at the citification of Ricky Skaggs in the 1985 video for "Country Boy".
 The improvisational-rock band Phish has performed their cover version of Uncle Pen over 200 times in the band's 30-year career.
"Blue Moon of Kentucky" is a waltz written in 1946 by bluegrass musician Bill Monroe and recorded by his band, the Blue Grass Boys.
 The song has since been recorded by many artists, including Elvis Presley.
 In 2003, the song was chosen to be added to the United States Library of Congress National Recording Registry.
"Wooden Heart" ("Muss i denn " "lit."
 Must I then) is a song best known for its use in the 1960 Elvis Presley film "G.I. Blues".
 The song was a hit single for Presley in the UK Singles Chart, making No. 1 for six weeks there in March and April 1961, but was not released on a single in the United States until November 1964, where it was the B-side to "Blue Christmas".
 Presley performed the song live during his Dinner Show concert at the Hilton Hotel in Las Vegas in 1975, a recording available on the Elvis Presley live album "Dinner At Eight".
"Blue Moon" is a classic popular song written by Richard Rodgers and Lorenz Hart in 1934, and has become a standard ballad.
 It may be the first instance of the familiar "50s progression" in a popular song.
 The song was a hit twice in 1949 with successful recordings in the US by Billy Eckstine and Mel Tormé.
 In 1961, "Blue Moon" became an international number one hit for the doo-wop group The Marcels, on the "Billboard 100 chart and in the UK Singles chart.
 Over the years, "Blue Moon" has been covered by various artists including versions by Frank Sinatra, Billie Holiday, Elvis Presley, The Mavericks, Dean Martin, The Supremes and Rod Stewart.
"When My Blue Moon Turns to Gold Again" is a song written by Wiley Walker and Gene Sullivan in 1940.
 They first recorded it in 1941.
 It has been recorded by Cindy Walker, Cliffie Stone, Elvis Presley, Sammi Smith, the Statler Brothers, Hank Thompson, Emmylou Harris, Eddy Arnold, Jim Reeves, Bill Monroe, and Merle Haggard, among others.
The Bluegrass Album is the nineteenth studio album, and the first bluegrass album by American country music artist Alan Jackson.
 It was released on September 24, 2013 via Alan's Country Records and EMI Nashville.
 Jackson wrote eight songs for the album.
 It also includes covers of The Dillards' "There Is a Time", John Anderson's "Wild and Blue" and Bill Monroe's "Blue Moon of Kentucky".
 Also included is a re-recording of "Let's Get Back to Me and You" from his 1994 album "Who I Am", marking the second time Jackson has included two versions of the same song on two different albums ("A Woman's Love" was originally recorded for "High Mileage" and was later re-recorded for "Like Red on a Rose").