Pop superstar George Michael's death at the age of 53 from suspected heart failure is being treated by police as "unexplained but not suspicious".
The 53-year-old, who rose to fame as the front man of Wham! and had chart-topping hits including Last Christmas, died peacefully at home, his publicist said.
The cause of the star's death was heart failure, according to his manager Michael Lippman.
Michael - whose real name was Georgios Kyriacos Panayiotou - sold more than 100 million albums throughout a career spanning almost four decades.
Big names from the world of entertainment have paid tribute to him after hearing about his death, which comes in a year that has seen the music industry lose some of its biggest stars including Prince, David Bowie and Leonard Cohen.
Sir Elton John posted a photograph of himself and Michael on Instagram, writing: "I am in deep shock. I have lost a beloved friend - the kindest, most generous soul and a brilliant artist. My heart goes out to his family and all of his fans."
Michael's former Wham! bandmate Andrew Ridgeley said he was "heartbroken at the loss of my beloved friend Yog", a nickname which refers to "Yours Only George".
He said: "Me, his loved ones, his friends, the world of music, the world at large. 4ever loved. A xx"
Friend Madonna paid her own tribute, posting an undated video on Twitter in which she embraced Michael on stage. In it she tells the audience: "He's a great songwriter and he makes very classy videos, like me."
Referencing several of his best known lyrics, she adds: "George, I want your sex, so be my father figure and I will have faith if we have to live hand-to-mouth. The diva himself."
Michael formed duo Wham! with Ridgeley in 1981, and went on to massive success, releasing a string of hit singles including Wham Rap! (Enjoy What You Do), Club Tropicana, Wake Me Up Before You Go Go, and Last Christmas.
They were the first Western pop act to visit China when they played there in 1985, before splitting in 1986, by which time Michael had already released a handful of solo singles.
On Sunday night, Thames Valley Police said they were called to a property in Goring-on-Thames shortly before 2pm, adding: "Sadly, a 53-year-old man was confirmed deceased at the scene.
"At this stage the death is being treated as unexplained but not suspicious. A post-mortem will be undertaken in due course. There will be no further updates from Thames Valley Police until the post-mortem has taken place."
The star's publicist said: "It is with great sadness that we can confirm our beloved son, brother and friend George passed away peacefully at home over the Christmas period.
"The family would ask that their privacy be respected at this difficult and emotional time. There will be no further comment at this stage."
As well as being known for his talents, Michael had a turbulent personal life, as brushes with the law and tales of drug use saw him hit the headlines.
He nearly died from pneumonia in late 2011, and after receiving treatment in a Vienna hospital, he made a tearful appearance outside his London home and said it had been ''touch and go'' whether he lived.
Doctors had performed a tracheotomy to keep his airways open and he was unconscious for some of his spell in hospital.
Meanwhile, Michael's 1990 album Listen Without Prejudice Vol. 1 had been set to be reissued accompanied by a new film featuring Stevie Wonder, Elton John and the supermodels who starred in the video to his hit single Freedom! '90.
The movie, with the working title Freedom: George Michael, was to be narrated by Michael and set to feature Mark Ronson, Mary J Blige, Tony Bennett, Liam Gallagher, James Corden and Ricky Gervais.
The record was his second solo album, after the hugely successful Faith, and was arranged, produced and almost entirely written by Michael, but did not feature him on the album cover.
It featured hits including Cowboys And Angels, Mother's Pride and Praying For Time and outsold Faith in the UK, where it went platinum four times but led to a court case with US record label Sony about Michael's frustration over how the album has been marketed. Michael lost the case.
Candles were lit outside Michael's north London home.
Kevin McDonagh, who lives nearby, came to pay tribute and said he remembers dancing with his wife to Michael's music when they were teenagers.
He said his children now, aged 15 and 17, have been listening to Michael's music all over the festive season.
Mr McDonagh, originally from Armagh, said: "He touched a lot of people. And in some point in your life you have to demonstrate your appreciation of talent. He was troubled but it doesn't take away from his talents."
He described Michael as a "man of the people".
Helen Bradbear, who also lives closeby, came to pay tribute to the star. "I just loved his music," she said, adding: "I think he was a very big-hearted, caring human being really."
She described his songs as "universally expansive", and said she woke up and felt "really shocked" by the news. "I think he was a great man," she said, adding: "He's an inspiring figure."
A man who just gave his name as Walter said he and his wife Avril have known Michael in the Highgate area for years.
He said Michael was a "big part of the community" and that he visited the couple's lifestyle and interior shop in the village.
"He did a lot for the village," he said, adding that the star was the driving force behind sorting a Christmas tree on a communal green area opposite his house.
Walter, who was out walking his dog Luna B, said Michael "loved dogs", but said he had not seen him for a while.
"He kept himself to himself. He was a private man," he said.