The Essential Backstreet Boys is the third compilation album by American pop group Backstreet Boys, released by RCA Records and Legacy Recordings as part of their "Essential" series.
 It was released on September 26, 2013 in the United Kingdom, and on October 22, 2013 in the United States.
 The album includes songs from the group's first seven studio albums, "Backstreet Boys" (1996), "Backstreet's Back" (1997), "Millennium" (1999), "Black & Blue" (2000), "Never Gone" (2005), "Unbreakable" (2007), and "This Is Us" (2009).
 It also includes the song "If You Stay" recorded for the 1997 film "Booty Call", and "Drowning" from their first greatest hits compilation, "The Hits – Chapter One" (2001).
The Hits – Chapter One, also known as Greatest Hits – Chapter One internationally, is the first greatest hits compilation released by American band, the Backstreet Boys.
 The album features fifteen of the group's classic hits, as well as one new song, "Drowning".
 "Drowning" was the album's only single, peaking at  4 on the UK Singles Chart and making the top 10 in most countries.
 A video album, featuring all of the videos from the release, was made available around the same time as the album.
 The album went to No. 4 on the US Billboard 200 chart and was certified platinum by the "RIAA".
 This was their second No. 4 album in the US following "Backstreet Boys" in 1997 and their fourth consecutive top-ten album in the US following "Black & Blue" in 2000.
Backstreet Boys: Show 'Em What You're Made Of is a 2015 American documentary film about the career of the American vocal group Backstreet Boys, released on January 30, 2015 in the U.S., and was released on February 26, 2015 in the UK and Europe, and March 28, 2015 for the rest of the world.
 It was directed by Stephen Kijak.
"Bigger" is a song by American boy band Backstreet Boys.
 It was released on November 29, 2009 as the second single from their seventh studio album, "This Is Us" (2009).
 The song was co-written and produced by collaborator and producer Max Martin.
 The band stated that the song was one of their best hits since "I Want It That Way", a song written and produced by Martin for the band in 1998.
 This was the last standard Backstreet Boys single released before Kevin Richardson rejoined the group.
"It's Christmas Time Again" is a Christmas song by American vocal group Backstreet Boys.
 The song was written by Backstreet Boys members Nick Carter and Howie Dorough along with Mika Guillory and Morgan Taylor Reid in early October 2012.
 It is the first song by the Backstreet Boys to feature Kevin Richardson's vocals in six years.
 Richardson left the group in 2006 and rejoined in 2012.
 It is also the first song released under the group's own label K-BAHN.
In a World Like This is the eighth studio album (seventh in the United States) by the Backstreet Boys, released in 2013 through the band's own record label K-BAHN.
 A follow-up to 2009's "This Is Us", it is the first album featuring all five original members since Kevin Richardson left the group in 2006 to focus on his family and pursue other interests.
 Richardson rejoined the group in 2012.
 It was also their first and only independent album since leaving their old label Jive Records in 2010.
 The album debuted at number five on the US "Billboard" 200, making the Backstreet Boys the first act since Sade to have nine US top 10 albums, and the only boy band to do so.
Kevin Scott Richardson (born October 3, 1971) is an American singer, songwriter, actor and model, best known as a member of the Backstreet Boys.
 Richardson was inducted into the Kentucky Music Hall of Fame along with his cousin and bandmate Brian Littrell on April 10, 2015.
The discography of American pop vocal group Backstreet Boys consists of eight studio albums, 28 singles, one live album, three compilation albums and 25 music videos. Formed in Orlando, Florida in 1993, the group consists of Nick Carter, Brian Littrell, Kevin Richardson, A. J. McLean and Howie Dorough.
 Richardson left the group in 2006 to pursue other interests, but rejoined in 2012.
 The Backstreet Boys released their debut single "We've Got It Goin' On" in 1995, which peaked at number sixty-nine on the "Billboard" Hot 100.
 The single, however, entered the top ten in many European countries.
 Their debut album, "Backstreet Boys", was released internationally in 1996, and was certified three times platinum in Europe, and diamond in Canada.
 In 1997, they released their second international album, "Backstreet's Back", which continued their international success.
 At the same time, they released their second self-titled album in the United States.
 It peaked at number four and eventually became the tenth best-selling album of the 1990s.
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.
Backstreet Boys is the self-titled debut U.S. studio album by the vocal-pop group Backstreet Boys.
 The release of this album coincided with the release of their second international album "Backstreet's Back".
 Their international debut album released in 1996 was also titled "Backstreet Boys", but it was not released in the United States.
 This second self-titled album was released only in the United States in 1997, making it their debut album in the country.
 It became one of the most successful debut albums of all time.
 The album peaked at number four on the "Billboard" 200 albums chart and has been certified 14× Platinum (Diamond) by the RIAA for sales to retailers, having sold over 14 million copies to date in the United States.
 This was also reported as the second highest seller in the past 14 years for Music Club sales back in 2003, selling 1.72 million units.

Question: Who rejoined the Backstreet Boys who was also inducted into the Kentucky Music Hall in April 10, 2015?
Answer: Kevin Richardson