But Prince was still on stage – and still captivating the exclusive group of about 200 fans who had gathered in an intimate penthouse loft to hear him perform.

Though he had taken about a two-hour break between sets, Prince was entering hour four in what would become a nearly five-hour musical extravaganza that not only included his own seminal hits like “Purple Rain” and “Little Red Corvette,” but also interpretations of music from Jimi Hendrix, the Beatles, The Rolling Stones and even Janet Jackson and India.Arie for good measure. (Fans paid $1,000 for the first jam session and $300 for the second: Proceeds went to charity.)

It’s this kind of magic that Prince tried to capture with “21 Nights,” a glossy coffee-table book published by Simon & Schuster that documents the glamorous rocker during his record-breaking, 21-night run at London’s 02 Arena last year. The book not only steals glimpses of his onstage performances, but also behind-the-scenes moments of the star and his band during the unprecedented concert stint.

“No one had ever sold out 21 nights in a row,” said photographer Randee St. Nicholas. “So I thought, ‘We should do a book surrounding this point in his life, because this is a great point in his life.'”

While his three-decades-long career has been meticulously chronicled, Prince is quick to point out, “Not by me – never by me. That’s someone else who’s on the outside looking in.” This time, it’s Prince – with St. Nicholas – telling the story, through his own frame of reference.

“This was a landmark event,” says Prince, sitting on the rooftop with the Manhattan skyline as his backdrop during a break from rehearsals before the evening’s musical marathon. “No one believed that it would do what it did. … Everyone tried to talk me out of it.”

Of course, Prince is used to proving skeptics wrong. These days, he’s regarded as a pioneer for artists’ rights and known for releasing music over the Internet. But when he left his longtime label Warner Bros. nearly two decades ago after a protracted battle over his creative path, and abandoned major record labels to release music on his own, he left everyone – from fans to musician insiders – wondering if he had lost his mind.

In recent years, he has re-linked with major record labels like Sony and Universal Music Group to release his albums, but isn’t sure any record is worth putting out in this era of piracy and illegal downloads. Though the book includes a CD, it contains no new songs, just classic hits and other songs from one of his signature jam sessions.

“Today, it’s not realistic to expect to put out new music and profit from it. There’s no point in trying to put new music out there and keep it from being (exploited),” he says.

And he now has disdain for the way the Internet has, in his view, subverted artists’ rights.

“The powers that be are abusing the copyright infringement,” he says. “You can’t sample Steven Spielberg; you don’t see his stuff up there, just old tapes of the Ohio Players, who can’t afford to defend themselves.”But while Prince exudes hints of frustration, he’s hardly bitter: These days, serenity and good-natured fun seem to be his mantra.

Though he professes shyness, the diminutive artist gives a warm hug as a welcome, and during his show – which had Spike Lee, Anderson Cooper and Dave Chappelle in the audience – he had fans laughing as he cracked jokes throughout (among his more memorable was referring to himself as Rihanna, an allusion to Internet gossip that the statuesque singer had been mistaken for Prince).

St. Nicholas, a longtime friend, says Prince’s conversion to the Jehovah’s Witness faith several years ago has helped him evolve into a more spiritual person – and a more open one, in comparison with his reputation as a moody recluse. But Prince’s public image has never been the real Prince that friends see behind closed doors, she adds.

“He’s shy. But he doesn’t necessarily hide or shield himself and attempt this mysterious persona that he has,” she says of the twice-divorced star.

“You know children? You never know what they are going to do one minute to the next? … That’s very much how he is,” she explains. “In a way it’s very open, because if you can just hang in that moment with him, and just go for it – you’re not worrying about the past.”

And at times, Prince isn’t even consumed with the present. While he talked about biblical implications to the recent stock market plunge (“that’s why I had to bring back this song,” he says as his band rehearses “1999” in the background), when it comes to a recent milestone, he’s decidedly nonchalant.

“How old are we really?” asks Prince, who turned 50 in June. “It’s about ascension. It’s not the other way. There’s nothing down about it. Everything is better.”

As an example, he points to the 21-night run in London: “I couldn’t have sold out 21 nights in London in the peak of my career; it would have been an impossibility,” he says.

“I look forward to these years where everything is just open sky. I wish this for every artist: freedom.”