Last January, Ella Henderson rang in a milestone for the ages. Miles from home, the UK native celebrated her 18th birthday with hit-maker Ryan Tedderin his Denver, Colo., home studio, recording what would become Henderson's debut single "Ghost."

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"It was just a very surreal time," Henderson tells ETonline in our latest installment of "Behind the Hit." The new series, which last week highlighted Hunter Hayes, asks artists to reflect on how their biggest songs came to life and what it’s meant for their careers.

Henderson caught the eye of Simon Cowell during a stint on The X Factor's ninth UK season in 2012. Viewers and judges were shocked when Henderson was sent home in sixth place, but Cowell still scooped up the talented singer-songwriter and signed her to a deal with his SYCO label.

"He constantly asks me, am I happy? Am I enjoying it? And it’s so nice for him to say things like that," Henderson gushed of Cowell. “To have someone with so much experience and so much advice, for him to have so much belief and faith in me -- to let me take my time and take me onboard at the age of 16 -- put a bit of self-confidence into me, which was exactly what I needed at that age. I was very shy.”

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Taking her time in the studio to nail the sound of her first album, Henderson posted a cover of Drake's "Hold On, We're Going Home" to YouTube. The video eventually made its way onto the radar of Tedder, who’s penned hits with Beyonce, Carrie Underwood, Kelly Clarkson and Adele, among many others.

"He got in touch with the label and was going back and forth, and eventually I ended up in the studio with him," Henderson recalled. "We wrote the chorus in like 10 minutes of meeting one another around a piano, which was a pretty exciting time because I instantly knew this was gonna be my first single."

"Ghost" was penned in the UK just before Christmas 2013. By the time Henderson turned 18 on Jan. 12, the track was recorded.

"I just remember it happening so quickly," she said. "I did three takes and ad-libbed over it – and that was it… It was only a year ago that I wrote it, and then to think what's happened since, it's crazy what can happen in a year."

Earlier this week, "Ghost" was certified Platinum in the U.S. in recognition of over 1 million singles sold. The song continues to climb the U.S. charts, recently cracking the iTunes Top 10, while the official music video has racked up more than 46 million views on Vevo. On the other side of the pond, "Ghost" is the UK’s fastest selling debut single by a new artist.

"[The song is] to represent something or someone that’s got a hold over you," Henderson said of "Ghost's" universal appeal. "You can't eat, you can't sleep, and it physically drains you. I think everybody has experienced that in some way or another, whether it be your boss at work or somebody who's getting you down in life."

Her debut album Chapter One debuted last month in the U.S. at No. 11 on the Billboard 200, and she's already planning for Chapter Two. "[I'm] getting back into the writing process and just keeping all them things going on the sidelines."

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There's no doubt that Henderson is one of our favorite rising divas, but find out how well she knows the classics with "Guess That Diva!" in the player below.

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