Ariana Grande has expressed her sorrow at the deaths of 22 people in an explosion after a show in Manchester.
The US star was not physically hurt, but posted a tweet saying: "Broken. from the bottom of my heart, i am so so sorry. i don't have words."
The blast happened just after the 23-year-old singer had finished performing at Manchester Arena on Monday evening.
Her manager Scooter Braun has also posted a statement, saying "our hearts are broken".
The singer was greeted by her family and boyfriend Mac Miller as she flew back to Boca Raton, Florida, on Tuesday, US media report.
The arena was packed with thousands of her fans at the time - including a large number of teenage girls, who make up most of her fan base.
Mr Braun continued: "Words cannot express our sorrow for the victims and families harmed in this senseless attack.
"We mourn the lives of children and loved ones taken by this cowardly act.
"We are thankful for the selfless service tonight of Manchester's first responders who rushed towards danger to help save lives.
"We ask all of you to hold the victims, their families, and all those affected in your hearts and prayers."
Who is Ariana Grande?
- Started on Broadway at the age of 15 and found wider fame on TV in Nickelodeon's sitcom Victorious
- Made the breakthrough with her music in 2014 with the single Problem, featuring Iggy Azalea, which reached number one in the UK and two in the US
- Other hits include Side To Side, featuring Nicki Minaj, which reached number four in the UK last year
- She has three American Music Awards, six Teen Choice Awards and four Grammy nominations
- She's in the middle of a European tour - she's already played Birmingham and Dublin and is due to be at the O2 Arena in London on Wednesday and Thursday
Fellow musicians sent messages of support and condolence, including Little Mix - who supported Grande on the US leg of her tour.
Olly Murs tweeted: "No one should go to a concert and never come home."
Demi Lovato said: "Tearing up imagining innocent concert goers losing their lives.. praying for everyone."
Lorde added: "Every musician feels sick & responsible tonight - shows should be safe for you. Truly a worst nightmare. sending love to Manchester & Ari."
As well as her forthcoming gigs in London, Grande has concerts scheduled in Belgium, Poland, Germany, Switzerland, France, Portugal, Spain, Italy and South America.
There is no official word as yet on whether those shows will go ahead.
Manchester Arena, meanwhile, is due to host three gigs by Take That later this week, followed by WWE, Kings of Leon and the Vitality Netball Superleague.
The venue, formerly known as the MEN Arena, has a maximum capacity of 21,000 - with around 18,000 for concerts.