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".
Michael, 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 paid tribute 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", an affectionate nickname used for the star.
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 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, Sir Elton and the supermodels who starred in the video to his hit single Freedom! '90.
An appeal for archive footage and imagery from fans including "mass Wham! hysteria" had been made on Michael's website in August, with a post on his official Facebook page saying: "George is personally seeking rare Wham! & George Michael photos and video and we need your help!"
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."
'Big part of the community'
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.
Meanwhile, at the music star's riverside home in Goring-on-Thames several floral tributes had been left for him.
One card, signed "Tracy", said: "Dear George, My heart is broken, you have gone too soon. Thank you for sharing your talent with the world.
"Some of my most precious and happiest memories have been watching you sing live and one of the best days of my life was being at Wembley for Wham's final concert and again when you sang at the new Wembley.
"I hope that you have finally found some peace and you know how much you were loved.
"Your music and spirit will live on.
"Forever in my heart, Tracy xxx."
Another card, which was anonymous, said: "George, thank you for your songs and your beautiful voice. We will miss you x."
Spandau Ballet star Martin Kemp and his wife Shirlie - a backing singer for Wham! with her musical partner Helen "Pepsi" DeMacque as part of the act Pepsi & Shirlie - have both paid tribute to Michael.
Kemp wrote on Twitter: "My whole family and I are devastated at the loss of our beautiful friend Yog! We will miss him so much! We are all heartbroken!"
Shirlie wrote that she is "beyond heartbroken".
She added: "Words cannot express how sad we all are, only last week I saw him laughing and happy. My heart is broken to lose someone so special."
Kemp previously revealed how Michael was responsible for his getting with Shirlie, to whom he has been married since 1988.
Michael introduced Shirlie to Kemp in the 1980s and joined them on their very first date.
Speaking to Piers Morgan on his Life Stories programme in 2014, Kemp said: "'He's a special person, George. He's been a good friend to us for years.
"'It's funny because I remember the first date that Shirlie and I ever went on. George came as a chaperone. I spent the whole evening trying to lose him so that me and Shirlie could sneak off somewhere and snog.
"He's a special person and he always will be."