For years, fans of the British boy band had only ever seen Tomlinson singing a few lines of "Hey There Delilah" by the Plain White T's as part of his 2010 audition for the competition series.
A new clip released Wednesday, however, shows that he actually kicked things off with a different song — and only changed his tune at the request of judge Simon Cowell.
"I love singing and this means so much to me, I just want to give it my best," Tomlinson, then 18, tells judges Cowell, Louis Walsh and Nicole Scherzinger.
With that, the "Back to You" musician says he aspires to be like singer-songwriter James Morrison, and dives into the 2007 Scouting for Girls track "Elvis Ain't Dead," none of which ever made the X Factor broadcast.
Tomlinson makes it through a verse and a chorus before Cowell stops the track and asks for another song, at which point the star begins "Hey There Delilah."
Nigel Waldron/Splash News Online Louis Tomlinson
Though Cowell assures him his second choice is a "much better song," Tomlinson admits that his nerves have gotten the best of him as each judge takes a moment to offer their critiques. "I'm so nervous," he exclaimed.
"Look, you know what, you're actually doing well, which is why we asked you to do a second song, right? So this is a better song for you," Cowell tells him.
Scherzinger, meanwhile, gives the teen an enthusiastic thumbs up, but notices he looks "defeated."
"Yeah, I can do so much better than that, honestly," the star, now 30, says. "Please just give me a chance."
The Pussycat Dolls alum eventually gives her seal of approval, saying: "I didn't really need you to be walking around the stage so much when you were singing because honestly, Louis, I really do believe you when you're singing, and I think that you have an amazing connection with music. So I just want you to stand there and to sing for us. But you know, I'm really happy I got to hear that second song because I really like you."
Though Tomlinson eventually made it through with three yeses, he was ultimately eliminated from the competition as a solo artist before being brought back to form One Direction alongside Harry Styles, Niall Horan, Liam Payne and Zayn Malik.
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As a band, the group placed third on the show, and went on to release five studio albums together before announcing an extended hiatus in 2015.
Over the last month, X Factor UK has been releasing extended cuts of all five members' auditions, starting with Harry Styles.
The "Watermelon Sugar" singer's clip included his never-before-seen take on Train's "Hey, Soul Sister," while Horan's featured his unaired version of "U Got It Bad" by Usher.
Tomlinson, Styles, Horan, Payne and Malik have each gone on to launch solo careers, and Tomlinson released Walls, his debut studio album, in 2020.
The singer said in a recent interview that he remembers his time in One Direction fondly and is "immensely proud" of his time with the group.
"I mean, it was an incredible thing to do and especially at such a young age," he told Australian talk show The Project. "Amazing memories, man, amazing."