James Corden and Olly Murs have consoled Louis Tomlinson after the One Direction star’s sister died aged 18 after suffering a suspected cardiac arrest.
Aspiring fashion designer Felicite Tomlinson died at her flat in Earl’s Court, west London, on Wednesday.
Her death is being treated as unexplained by police.
Corden offered his support to 27-year-old Tomlinson.
He tweeted: “Such incredibly sad news today.
“You’re not on your own in this Louis Tomlinson So many people are pulling for you and your family right now”.
Murs, who found fame on the X Factor one year before One Direction, posted a message to Twitter.
It read: “Absolutely heartbreaking hearing the news of Louis sister Felicite sending my love to him & all his family right now! Awful news.”
It comes after Tomlinson’s mother Johannah Deakin died from leukaemia in 2016 at the age of 43.
Other celebrities, including Westlife singer Brian McFadden, rallied around Tomlinson.
McFadden wrote: “This is so sad. This boy has had it tough”.
US singer Charlie Puth also tweeted, saying: “Prayers to Louis Tomlinson. I can’t imagine how hard it is right now.
“Love to you brother I’m so sorry and my prayers are with you.”
Watford boyband Rak-Su, who won the fourteenth series of the X Factor before Tomlinson debuted as a judge, sent their sympathies.
They said: “Our condolences and prayers go out the Louis Tomlinson and his family at this time.”
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.
“A female believed to be aged 18 was pronounced dead at the scene.
“A post-mortem examination will take place in due course.”
Felicite was well known on social media and regularly shared posts with her 1.3 million followers on Instagram.
On January 30, she posted a picture of a row of tattoos on her forearm, which she said were the initials of all her siblings.
Her last post came just four days ago.
It is understood that Tomlinson, who was reportedly in London for a now-cancelled appearance on Friday night’s Comic Relief, was told of her death on Wednesday.
The siblings’ mother died at the Royal Hallamshire Hospital in Sheffield on December 7 2016 after being diagnosed with leukaemia earlier that year.
Following her death, Tomlinson released the song Just Hold On – his debut solo single – in her honour, and he performed it on the X Factor just days later.
At the time he described the performance as “harder than I ever imagined”.