Felicite Tomlinson attends "The Spongebob Movie: Sponge Out of Water" screening on March 15, 2015 in London, England.
In a statement, Scotland Yard said: "Police were called by London Ambulance Service at 12.52 on Wednesday, March 13 to a residential address. following reports of a female in cardiac arrest". Paramedics tried to revive her but were unsuccessful.
Two ambulance crews reportedly responded to a 999 call (London's emergency call number), as well as a paramedic and medic in a separate vehicle, The Sun said.
Felicite Tomlinson passed away on Wednesday in London in the United Kingdom, according to TMZ.
Police officers are investigating the teenager's death, which they are now treating as "unexplained".
The teen was a budding fashion designer, reportedly set to launch her own clothing line in the future.
The tragedy is a huge blow for Louis, who lost his mother, Johannah, to cancer in December, 2016.