Félicité, a social media influencer, was found dead in her London home on Wednesday after a suspected cardiac arrest.
Tomlinson, who was a social media star in her own right with almost 1.3 million Instagram followers, was reportedly found unconscious at her apartment in Earls Court, West London on Wednesday, according to The Sun. The cause of her death is still to be confirmed, but it is reported to have been a suspected heart attack.
Actor and talkshow host James Corden said the news was "incredibly sad" and tweeted to Tomlinson that he is "not on your own in this".
Felicite Tomlinson has tragically died aged 18.
This news comes just a few years after the tragic passing of their mother, Johannah Deakin, who had leukemia.
They said: "Our condolences and prayers go out the Louis Tomlinson and his family at this time".
Louis Tomlinson with Liam Payne
How did Louis Tomlinson's sister Felicite Tomlinson die?
Louis is yet to react publicly to the tragic news but according to British newspaper The Sun the singer is "devastated and distraught" by the loss of his sibling who was "lovable, caring, bright and beautiful".
The results of a full post-mortem examination will be released in days.
Felicite was well known on social media and regularly shared posts with her 1.3 million followers on Instagram.
Louis has cancelled his appearance on tonight's Comic Relief following the tragedy.
At the time he described the performance as "harder than I ever imagined".
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