Is Michael Bublé the world's most fancied man?

Up on the penthouse level of Waterstone's Piccadilly, they're preparing for chaos. 'Anyone wet themselves yet?' whispers a member of the store's book-signing team. It appears not. Outside, the fans have been queuing since 6am. The lucky first 300 will have their shiny new coffee-table tome signed, and approximately seven seconds of face time with the object of their lusty affection. For the staff at Waterstone's incontinence is a probable hazard. So when the Canadian Sinatra comes to town for a book-signing, they're on standby with boxes of tissues and buckets and mops. Already on this visit to the UK Michael Bublé has taped an appearance on The Jonathan Ross Show; next he must begin rehearsals for an ITV festive special and in between he has to promote his other new release, an album of Christmas songs.

'Things have changed,' Bublé, 36, reflects in his Soho hotel a few days after the Waterstone's event in support of his glossy memoir Onstage, Offstage. 'If that signing was during my first or second year in the business, it would have been "Hey young man!" ' he says, affecting Grandpa Simpson's voice. 'I'd be going, "Who can I sign it for?" and the person would be going, "I forget my name" But at Waterstone's it was all 15-year-old girls.'

He tells me how he 'pushed' his record label to change how it marketed him - his last album, 2009's Crazy Love, featured the bouncy hit single 'Haven't Met You Yet', a song that (unusually for this interpreter of standards) he co-wrote himself. Whereas his paymasters persisted in seeing him as a modern(ish) reboot of Ol' Blue Eyes, a cutesy crooner, he said, no, he was a pop singer. 'And it was nice for me to break free.'

Now he's proud of his 'eccentric and eclectic' audience. The UK is Bublé's biggest international market, accounting for a good chunk of the 30 million albums that this latest 'Groover from Vancouver' has sold since his 2003 debut. But he's an arena-filling megastar all over the world. 'At my shows now I look out there and I see 11-year-old kids having a birthday party, 18-year-old boys trying to get laid at the concert, couples from 25 to 45, old, black, white, gay, straight - the whole lot'

I first met Bublé in his kitchen in late 2007. It was lunchtime and he had come barrelling into his $5 million, 7,113sq ft home in Vancouver, toting bags of Chinese food. He was instantly friendly; a regular, ice-hockey-loving likes-a-drink-or-five Canadian dude in a baseball cap. Albeit one who - once he'd slid into a tux and gelled his hair - was a titan of mega-selling easy-listening albums. And who, at the time, was sharing his heart and home with the English actress Emily Blunt. I was there to interview Blunt, and Bublé was more than happy to take a back seat, let me snoop around his McMansion, and allow me to quiz his girlfriend about their relationship. 'Michael's not really that sort of smooth, sophisticated guy,' the star of The Devil Wears Prada and The Young Victoria told me. 'He's a bit rough. He's my bit of rough! And he's hilarious. We laughed a lot together from the get-go. And we've laughed a lot ever since. Now I've got a nice house as well. So we're laughing in our nice house.'

I met him again two years later. Same home, different girlfriend: Blunt had chucked Bublé. A forcefully candid bloke, he'll admit that he wasn't the best - most faithful - boyfriend. He's loath to go into details, but one girl, reputedly a long-standing 'friend with benefits', went public with claims of bedding the star. He had already conceded to me that one of the reasons that as a teenager he began singing standards, rather than pop or rock, was to 'get laid This is why I wanted to be different and why I wanted to have power and fame and money; because I wanted to be attractive to the opposite sex.' Yet once he had it, all that went to his head. He had hurt people, and been hurt, and was appalled by his own behaviour. But now, honest guv, he had turned over a new leaf.

By then he was dating Luisana Lopilato, a cute-as-a-button Argentine actress 12 years his junior. A one-time pop star, she's starred in soaps, telenovelas and movies. They had met at one of his concerts in Buenos Aires. His Spanish was nonexistent, and her English was heavily accented, but it was obvious that they were besotted with each other. As we enjoyed late-night drinks on his patio - great views of Burrard Inlet, and of Bryan Adams' old pad - the pair of them joked about which Argentine tennis player it was that she had previously dated (it was Juan Monaco, not Juan Martin del Potro). 'If he cheat on me, I keel heem,' Lopilato said to me, before admitting that she had strong feelings for Jack (Matthew Fox) from the television series Lost. 'Yeah, twice when we've been making love she's called me Jack!' Bublé hooted.

The couple wed earlier this year. Three times. Two ceremonies took place in Buenos Aires, one in Vancouver. His wife is a huge TV and film star in South America, and is the face of the new Ultimo lingerie campaign, and her schedule is almost as crazy and itinerant as his. So how is married life treating him? 'You know what's weird? I think I've found it easier. I do! I think we were both scared. I think everybody is when they get married It's funny: we were married for something like a week and we were at Disney World in Florida on our honeymoon.' They went to Disney World for their honeymoon? 'We went to a bunch of places,' he clarifies. 'Israel, Spain, Venice, Disney World. And we were sitting there on the little Main Street in Disney World, kids so happy, people walking around, and we literally stopped and looked at each other and said: "I think we made a mistake." I think it was that moment that it hit us - the finality of what we'd done Like, when we used to fight, like every couple, you know you get real pissed off about something and you say, "F***, that's it, I'm outta here." Well, these threats are no longer made. Because there is no getting out.'

Is he saying that they made a mistake by getting married? He laughs. 'Both of us looked at each other and said, "Oh God we now have some reservations about each other." So we hit that thing that day. And I can honestly say, every day after, it got better. Because you start to accept it, and we stopped panicking, and you start to breathe it in and start to realise, "Ah, this is actually better, we're not fighting any more" I think it's too easy to quit on a relationship.' So is his relationship stronger now? 'Definitely,' he says emphatically. 'Most definitely.'

Another day, another London engagement. Bublé is at Elstree Studios, running through rehearsals for his Christmas special for ITV. Gary Barlow has already visited the mocked-up living-room set (roaring fire, giant Christmas tree, huge candles, 36-piece orchestra) for a duet. 'I thought he'd be nervous,' says Bublé. 'It can be hard coming on to someone else's show. But straight away, he's a funny f***er. He knocks at the door, I open it, act all surprised and delighted, and first thing Gary says is, "Aren't you gonna take my coat?"'