Felicite Tomlinson, who was a model and influencer with over 1.4 million followers, is believed to have collapsed at her home in London on Wednesday, March 13.
X Factor winners Rak-Su also offered their prayers for the family.
Felicite Tomlinson has tragically died aged 18.
Our deepest condolences are with Tomlinson and his entire family during this incredibly tragic time.
Her death comes shortly after Louis released a new song titled "Two of Us" about him and his mom which included the heartbreaking lyrics: "You'll never know how much I miss you/the day that they took you/I wish it was me instead".
A person who was with her called 999, according to the Sun newspaper.
Felicite Tomlinson passed away on Wednesday in London in the United Kingdom, according to TMZ.
Family sources tell the news outlet that the teenage fashion designer, known as Fizzy, had no prior history of heart trouble and was actually enjoying a bout of good health after giving up alcohol and cigarettes at the beginning of the year.
Her last post came just four days ago.
American singer-songwriter Charlie Puth said he is sending "prayers" to Tomlinson and added: "I can't imagine how hard it is right now".
He had been scheduled to perform his new single Two Of Us, which was written in honour of his late mother, on Comic Relief on Friday (March 15), but has now cancelled the appearance.
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