The 17-year-old has criticised his mentor Louis for vocalising his support for rival Sam, and also claimed that Gary "never liked him" while competing on the show.
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Nicholas McDonald with mentor Louis Walsh
The Daily Mail quotes him as saying: "Gary had a problem with me throughout the whole show. He never seemed to like me and whenever I gave a good performance he would pick up on the smallest things in the world.
"I was disappointed with Louis saying, 'Vote for Sam and her single everyone.' It felt like Sam was getting all the love."
Nicholas' mum Eileen McDonald also laid into Louis, adding to the Daily Record: "I thought it was very unprofessional but Louis sometimes says things and doesn’t think about it.
"I thought, ‘What is he saying that for?’ I thought it’s like Sharon voting for Nicholas, but it doesn’t matter.
"Nicholas is still a winner. No matter what, he’s made for life."
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X Factor winners
Series One, 2004(01 of12)
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Won by: Steve BrooksteinMentor: Simon CowellRunner up: G4 (credit:Rex)
Series Two, 2005(02 of12)
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Won by: Shayne WardMentor: Louis WalshRunner up: Andy Abraham (credit:Rex)
Series Three, 2006(03 of12)
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Won by: Leona LewisMentor: Simon CowellRunner up: Ray Quinn (credit:Rex)
Series Four, 2007(04 of12)
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Won by: Leon JacksonMentor: Dannii MinogueRunner up: Rhydian Roberts (credit:Rex)
Series Five, 2008(05 of12)
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Won by: Alexandra BurkeMentor: Cheryl ColeRunner up: JLS (credit:Rex)
Series Six, 2009(06 of12)
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Won by: Joe McElderryMentor: Cheryl ColeRunner up: Olly Murs (credit:Rex)
Series Seven, 2010(07 of12)
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Won by: Matt CardleMentor: Dannii MinogueRunner up: Rebecca Ferguson (credit:Rex)
Series Eight, 2011(08 of12)
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Won by: Little MixMentor: TulisaRunner up: Marcus Collins (credit:Rex)
Series Nine, 2012(09 of12)
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Won by: James ArthurMentor: Nicole ScherzingerRunner up: Jahmene Douglas (credit:Rex)
Series 10, 2013(10 of12)
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Won by: Sam BaileyMentor: Sharon OsbourneRunner up: Nicholas McDonald (credit:Rex)
Series 11, 2014(11 of12)
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Won by: Ben HaenowMentor: Simon CowellRunner up: Fleur East (credit:Syco/Thames/Corbis)
Series 12, 2015(12 of12)
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Won by: Louisa JohnsonMentor: Rita OraRunner up: Reggie N Bollie (credit:Syco / Thames / Corbis)