Question: Who replaced the singer in S Club 8 and The Saturdays as a host of The Xtra Factor?

Context articles: X Factor (Italy series 6)
The X Factor (UK series 12)
The X Factor (UK series 13)
The X Factor (UK series 14)
X Factor (Denmark season 6)
X Factor (Denmark season 7)
Marc Scarpa
Sarah-Jane Crawford
Rochelle Humes
The X Factor (UK series 11)

X Factor is an Italian television music competition to find new singing talent; the winner receives a € 300,000 recording contract with Sony Music.
 Before the start of the auditions process it was confirmed that Simona Ventura, Morgan, Elio and Arisa would be confirmed as judges and mentors; also Alessandro Cattelan returned as host, whilst Max Novaresi and Brenda Lodigiani return to host "Xtra Factor".
 The sixths series began airing on Sky Uno on 20 September and ended on 7 December 2012.
The X Factor is a British television music competition to find new singing talent.
 The twelfth series began airing on ITV on 29 August 2015 and ended on 13 December 2015.
 The judges were Simon Cowell, Cheryl Fernandez-Versini, who returned for their respective ninth and fifth series as judges, series 9 guest judge and former "The Voice UK" coach Rita Ora, and BBC Radio 1 DJ Nick Grimshaw, with Grimshaw and Ora replacing Louis Walsh, the only judge who had been on the show from its inception in 2004, and Mel B.
 It was presented by Caroline Flack and Olly Murs, who had both previously co-presented spin-off show "The Xtra Factor" on ITV2 and replaced Dermot O'Leary, who left after eight series.
 Rochelle Humes and Melvin Odoom presented "The Xtra Factor", replacing Sarah-Jane Crawford.
 Louisa Johnson was announced as the winner on 13 December 2015, making Ora the winning mentor.
The X Factor is a British television music competition to find new singing talent.
 The thirteenth series began airing on ITV on 27 August 2016 and ended on 11 December 2016.
 Dermot O'Leary returned to present the main show on ITV for the ninth time, after having quit the previous year.
 Simon Cowell was the only judge from the 12th series to return; Nicole Scherzinger, Sharon Osbourne and Louis Walsh all returned, replacing Cheryl Fernandez-Versini, Rita Ora and Nick Grimshaw.
 Matt Edmondson and Rylan Clark-Neal replaced Rochelle Humes and Melvin Odoom as hosts of "The Xtra Factor", which was rebranded as "The Xtra Factor Live" and was broadcast live twice every week, with Roman Kemp making appearances as a digital presenter and social media reporter.
 Matt Terry was announced the winner on 11 December 2016, making Scherzinger the winning mentor for the second time.
 Saara Aalto came second.
"The X Factor" is a British television music competition to find new singing talent.
 The fourteenth series began airing on ITV on 2 September 2017, presented by Dermot O'Leary.
 For the first time in seven years, the judging panel will remain the same, with Simon Cowell, Sharon Osbourne, Nicole Scherzinger and Louis Walsh returning.
 This is the first series not to include companion show "The Xtra Factor", after it was cancelled in January 2017.
 as well as the first to be sponsored by Just Eat, with the show having being sponsored by TalkTalk since 2009.
 Its replacement is a programme called "Xtra Bites" presented by Becca Dudley on the ITV Hub.
 It is also the second time the show has premiered in September, rather than August, since the first series in 2004.
X Factor is a Danish television music competition to find new singing talent.
 The sixth season premiered on December 28, 2012 on DR1 and ended on March 22, 2013.
 Signe Molde replaced Lise Rønne as host, while Emil Thorup hosted new spin-off show "Xtra Factor".
 Thomas Blachman returned for his fifth season as judge, while Ida Corr and Anne Linnet joined the judging panel as replacements for former judges, Pernille Rosendahl and Cutfather.
X Factor is a Danish television music competition to find new singing talent.
 The seventh season premiered on January 3, 2014 on DR1 and ended on March 28.
 Eva Harlou replaced Signe Molde as host.
 Thomas Blachman returned for his sixth season as judge and was rejoined by Lina Rafn and Remee, reinstating the original judging panel from seasons 1 and 2.
 Rafn and Remee rejoined the judging panel as replacements for former judges, Ida Corr and Anne Linnet.
 Spin-off show "Xtra Factor" did not return.
Marc Scarpa (born September 25, 1969 in New York City) is an American entrepreneur, producer and director specializing in live participatory media.
 He is an executive board member and the founding New York Chair of the Producers Guild of America New Media Council and a recipient of the Marc A. Levey distinguished service award.
 Scarpa has received a Webby Award in 2010 for Best Event / Live Webcast for his work on the 52nd Annual Grammy Awards, a Cannes Bronze Lion for Branded Content and Entertainment for the X Factor Pepsi Digital Preshow and Xtra Factor App and four Social TV Awards including Best of Show for X Factor Pepsi Digital Preshow and Xtra Factor App.
 Additionally, he has been a panelist for conferences such as NATPE, X-Summit, LTE North America, Digital Hollywood and Canadian Music Week among others.
Sarah-Jane Crawford is an English television and radio presenter, actress, voice-over artist, and DJ best known for her radio work with BBC Radio 1Xtra and television work with E! Network (which she is currently a host for), ITV2 on "The Xtra Factor", BBC and Channel 4.
 Crawford has also presented and appeared a number of shows for the Disney Channel and MTV.
Rochelle Eulah Eileen Humes (née Wiseman; born 21 March 1989) is an English singer and television presenter, best known for her work in pop groups S Club 8 and The Saturdays.
 Humes has achieved six Top 10 hits with S Club 8 and thirteen Top 10 hits with girl group The Saturdays, including number-one hit "What About Us".
The X Factor is a British television music competition to find new singing talent.
 The eleventh series began airing on ITV on 30 August 2014 and finished on 14 December 2014.
 Dermot O'Leary presented his eighth series of the main show on ITV and Sarah-Jane Crawford presented spin-off show "The Xtra Factor" on ITV2, replacing Caroline Flack and Matt Richardson.
 Louis Walsh was the only judge from series 10 to return and was joined by former judges Simon Cowell, and Cheryl Fernandez-Versini, and new judge Mel B.
 Sharon Osbourne, Gary Barlow and Nicole Scherzinger left after series 10.
 Former judge Tulisa returned as a guest judge for the final on 13 December due to Mel B being ill.
 The series also saw the lower age limit decreased from 16 to 14, as it was in series 4 and 5.
 This was Walsh's final series as a judge before returning in series 13.
 It was also the only series in which Mel B was a main judge.
 It was O'Leary's final series as presenter on the main show, as he announced on 27 March 2015 that he was leaving to pursue other projects, before returning in series 13.
 On 11 May, Crawford also confirmed via Twitter that she would leave her position as "The Xtra Factor" presenter.