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.
Tomlinson's mother, Johannah Deakin, died from leukemia in 2016.
Her fans became anxious about her weight loss late in 2018, but she explained the body transformation by saying, "Getting back to eating healthy and exercising using @pumpup app while I'm away".
And as the family grieves during this heartbreaking time, celebrities and close friends of Louis are reaching out to be there for the star.
Dancing On Ice star Brian McFadden continued: "This is so sad".
Scotland Yard said police were called by London Ambulance Service at 12:52 on Wednesday 13 March to a residential address following reports of a woman having a cardiac arrest.
They said: "Our condolences and prayers go out the Louis Tomlinson and his family at this time".
Felicite had 1.3 million followers on Instagram, where she posted lifestyle photos and video.
He has canceled his scheduled appearance on UK TV for the yearly charity event Comic Relief. "It's just the biggest tragedy and everyone wants to be there for Louis, who is the leader of his family since the loss of his mother and always there for all his siblings".
Louis released a song last week which was inspired by the grief he felt over his mum's death.