On Wednesday, Félicité passed out after a suspected heart attack at her studio apartment in Earls Court, West London, The Sun reports.
A friend, who was with Félicité at the time of the incident, immediately dialed 911.
When emergency responders arrived to the home they attempted to resuscitate Félicité, however, it was too late. She was pronounced dead at the scene, The Sun and The Daily Star report. She was 18.
Before her sudden death, Félicité, who was also known as Fizzy, worked as a model and influencer with over 1 million followers on Instagram.
Her last post was on March 10. “Don’t know why I look so shocked,” Félicité captioned the shot, which shows her posing in a mirror wearing a black one-shoulder top and blue jeans.
Louis, 27, has not yet addressed his sister’s death publicly.
A representative for the singer did not immediately respond to PEOPLE’s request for comment.
“Félicité was an absolutely adored young woman who was loved by Louis and her whole family,” a source close to the family told The Sun.
“They are totally devasted as you can imagine. She had so many friends and was such a positive happy person. It’s a massive loss to the world.”
At this time, Félicité’s exact cause of death is unknown.
Félicité’s death comes after their mother Johannah Deakin died of Leukemia on Dec. 7, 2016. She was 43.
“Johannah was first and foremost a truly amazing mother to seven children – Louis, Lottie, Félicité, and two sets of twins, Phoebe and Daisy and Ernest and Doris — whose individual talents and success are testament to the principles and beliefs she instilled in them,” Deakin’s husband Dan Deakin said in a statement at the time. “She was also an incredibly proud grandmother to [Louis’ son] Freddie.”
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“Incredibly selfless, she would always look to put other people before herself,” Dan continued. “She desired nothing more than for everyone around her to be happy and loving. She worked tirelessly on numerous charity campaigns, creating memories for many individuals and their families.
“It wasn’t uncommon for Johannah to hear through the media of an individual in need of assistance, and she would immediately make it her objective to get that person what they often desperately needed, and rarely without success. These are the things that made Johannah happy and content in life, and all of which for me made her simply the perfect wife and best friend to face each day with.”
Earlier this month, Louis paid tribute to his late mother in “Two of Us” — the first single off his debut album.
The song is a deeply personal and emotional pop ballad about the bond the two have, even after her death.
It begins by Tomlinson addressing Deakin directly, admitting that the day she died he wished “it was me instead.” However, after mourning her loss, Tomlinson began to take the lessons he learned from her and focus on the positives.
“I will keep you day and night, here until the day I die / I’ll be living, one life for the two of us,” he sings, in the chorus. “I will be best of me, always keep you next to me / I’ll be living one life for the two of us.”