Singer David Bowie has released a new single on his 66th birthday, following years of silence and speculation.
The glam-rock legend has released the recording Where Are We Now? as a video and download. It will be followed by a new album, The Next Day, in March.
Bowie has not performed live since 2006 and has rarely been seen in public since then.
The new track was recorded in New York and produced by the singer's long-time collaborator Tony Visconti.
Speaking to the BBC, Visconti admitted that keeping the project a secret has been difficult.
"People have asked what I've been working on and I've said 'I can't tell you... a mystery project... Project X,' so its such a relief that its out on that level."
Visconti continued: "The material is so strong and beautiful - if people are looking for classic Bowie they'll find that on this album, but if they're looking for innovative Bowie, they'll find that on this album too. It's all there."
Bowie's long absence from the industry and heart surgery in 2004 had prompted speculation about his health. However, Visconti insisted the singer "is extremely healthy and rosy cheeked."
"His stamina is fantastic," he added.
The single's appearance online was "a genuine surprise", said John Wilson, presenter of BBC Radio 4's Front Row.
"He's a proper artist. He doesn't release records because it's time for another record. He releases records when there's something for him to say."
Where Are We Now? is a simple, unfussy ballad - Bowie singing mournfully over a piano motif that slowly builds to an understated coda.
The song includes several references to the city of Berlin, where Bowie and Visconti produced a critically-acclaimed trilogy of albums - Low, Heroes and Lodger - in the 1970s.
"If you listen to each of the verses, there are lyrical references to Berlin, to Potsdamer Platz, to Nuremberg Strasse," said Wilson. "Places where he lived when he was making those albums. And there is an elegiac quality. There's a sadness, I think. A weariness to his voice."
The artwork for the new album, which has surfaced on iTunes, is an altered version of the cover to Heroes, suggesting a further connection to the Berlin Trilogy.
By breaking his 10-year musical silence, Bowie unsurprisingly prompted a flurry of praise on Twitter.
"I'm so insanely excited," journalist Caitlin Moran wrote. "It's like hearing King Arthur's voice from the cave."
Comedian David Walliams added: "I love that Bowie has kept his mystique. No word from him for years and then out of nowhere this beautiful song appears.
"I wonder whether Bowie will go on Loose Women to promote it?"
Music fan Chris Lilley wrote: "It's quite an elaborate way to apologise for not performing at the Olympics."
While Bowie's son, film director Duncan Jones, chipped in: "Would be lovely if all of you could spread the word about da's new album. First in ten years, and its a good 'un!"
Acknowledging the stealthy release of the single, the pop star's press representative said in a statement: "Throwing shadows and avoiding the industry treadmill is very David Bowie".
The Space Oddity star, it continued, was "the kind of artist who writes and performs what he wants when he wants".
Where Are We Now? is accompanied by a video directed by multimedia and installation artist Tony Oursler, which harks back to Bowie's time in Berlin.
The promo, which can be viewed via the singer's website, features his face projected onto the body of a puppet.
The face of a woman is projected onto the mannequin beside him, with Bowie appearing in more conventional form later on in the video, clutching a notebook and wearing a T-shirt with the logo for the classic operetta Song Of Norway.
Bowie, who was last reported to be living in New York with his wife and daughter, has not released material since his 2003 album Reality.
In September, the singer denied reports he was involved in an upcoming exhibition at the Victoria and Albert museum in London charting his career.