The Instagram star, who had amassed 1.4 million followers on the social media site, was just 18 years old at the time of her death.
Louis is said to be "devastated and distraught" by the tragic news, only three years after his mother died from leukaemia.
Felicite Tomlinson passed away on Wednesday in London in the United Kingdom, according to TMZ.
Other celebrities, including Westlife singer Brian McFadden, rallied around Tomlinson.
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X Factor winners Rak-Su also offered their prayers for the family.
A Metropolitan Police spokesman said: "Police were called by London Ambulance Service at 12.52pm on Wednesday, March 13 to a residential address in SW5 following reports of a female in cardiac arrest".
It's the second tragedy to hit the Tomlinson family in recent years.
Despite attempts to resuscitate Tomlinson, she was pronounced dead on the scene, TMZ said. "A post-mortem examination will take place in due course".
Her last post came just four days ago.