Louis Tomlinson's 18-year-old sister Félicité has died of a suspected heart attack, the Met Police said.
It's reported she collapsed in her home after a suspected heart attack at her fourth-floor studio apartment in Earls Court, West London, Wednesday lunchtime.
The person she was with called 999 immediately as two ambulance crews attended the address along with a paramedic and single responder medic in a car.
Although the crew tried to resuscitate Félicité, she was pronounced dead at the scene.
It's reported that police attended the scene to establish whether there were any suspicious circumstances.
“Sadly, despite the efforts of our medics, a person died”
London Ambulance Service
A post-mortem examination and toxicology tests will be carried out following the tragic death.
The teen's Instagram, which has more than 1.3million followers, has already started being flooded with tributes.
It's reported that, understandably, Louis is "devastated and distraught" by his sister's death.
A Met Police spokesman told The Sun: "Police were called by the London Ambulance Service at 12.52pm to a residential address in SW5."
The London Ambulance Service said: "We were called at 12.51pm.
"We sent two ambulance crews, a single responder in a car and an advanced paramedic to the scene.
"Sadly, despite the efforts of our medics, a person died."
Félicité's death comes just three years after the death of their mother Johannah Deakin.
Johannah died at the age of 43 in 2016 of leukaemia.
Louis had been scheduled to perform a tribute song to his mum for Comic Relief, but reportedly pulled out after the death of his sister.
In the lyrics, Louis sings: "You'll never know how much I miss you. The day that they took you, I wish it was me instead."
Louis has three other sisters – Charlotte "Lottie", Daisy, Georgia and Phoebe.