When I ask him about money and how it might be possible to appreciate life's smaller pleasures when you can have anything you want, he says: "I grew up in Tennessee. My mother told me it's uncouth to talk about money. I feel weird talking about it."
If this is a swerve, then his much-lauded performance in the Oscar-winning The Social Network (he played Sean Parker, the founder of Napster) by David Fincher was not a one-off: his face is a more-or-less convincing knot of embarrassment.
On my way to meet him, a photograph of Timberlake leaving the BBC had stared out at me from the pages of a newspaper. Is it impossible for him to be anonymous? It strikes me, looking at him now, that he has the kind of looks - weirdly unmemorable, though obviously I don't spell this out - that could allow him to wander unnoticed, if only he were willing to try it. "I don't know," he says, uncertainly. "I've never analysed my face. I think I know what you mean. I guess it's easier to go places when there's no event, when you're not working." He shrugs. "I think I struggled with [fame] more in my early 20s, trying to make sense of it ... But then you realise that you can't make sense of it, and you just have to let it all go."
So if it - the fame, the recognition - stopped tomorrow, would that be a relief, or would it, in fact, be awful - a painful loss, a kind of living death? "Sure, I'd be okay with it. I don't wake up and feel famous. I just love what I do."
Like the Monkees' Davy Jones or Mark Owen from Take That, for a certain number of people Timberlake will always be a boy, for all that he is now 30. He joined the band 'N Sync in 1995, aged just 14, and the group's first album, released three years later, sold 11 million copies.
Miraculously though, he has since managed to put some distance between himself and his astonishingly successful pop career - even as a solo artist, his albums generated top 10 single after top 10 single - thanks to his role as Parker in The Social Network, a gig for which he had to audition more than once. (Yes, there were other films before, but who honestly remembers Model Behaviour or The Love Guru?)
It's almost impossible to win credibility in one world when you are known in another - particularly if that other is the land of pop. So he has plainly been exceedingly clever - or at least, that's how it looks from the outside.
He laughs. "I wish I could take the credit for it. But it wasn't like that, though I agree that The Social Network was a breakthrough. I have a running joke with friends that I should have a business card that says: 'David Fincher put me in a movie'. It was thrilling being nominated for awards, because I felt the sense of doubt in people when I was cast. And it's true that I auditioned numerous times. But I felt I could do something with it, something subtle. The thing is, my idols have always been the types of guys who could do anything: Gene Kelly, Fred Astaire, Sinatra, Dean Martin and when you look up to people like that, you don't accept that you need to be compartmentalised."
So is acting to be his only career now? Friends With Benefits is his second film this year (the first was Bad Teacher, co-starring his ex-girlfriend, Cameron Diaz). He looks uncertain.
"I wasn't trying to make a point. They [the films] came at an opportune time, and they all seemed to be different characters, and I wouldn't have passed them up. Friends With Benefits feels like a two-hander to me, but it is a big movie, and this is the first straightforward male I've been able to play. I would describe my character in The Social Network as a kind of sociopath. I would describe my character in Bad Teacher as ... just a weirdo. But this is a male's male."
Hmm. Timberlake is okay at comedy, as anyone who has seen his "Dick in a Box" skit for Saturday Night Live will know (it's on YouTube, if you haven't).
But I fear he was fighting a losing battle in the case of Friends With Benefits, in which he plays a designer at GQ magazine in New York who enjoys a lot of violently athletic, no-strings, "no emotions" sex with his headhunter friend, Jamie (played by Mila Kunis, late of Black Swan) until, inevitably, they fall in love. Naturally, I don't tell him this, and so, for a while, he burbles happily on about the closed set, about how when the gaffer and the grip sniggered, he knew he had hit the right note, and about the fact that he pushed for the film to have an R-rating. He can, bless his heart, still recite great swathes of its (exceedingly lame) script.
"I keep getting the comment that Mila and I had a lot of chemistry, and we do, but I think you also have to get the rhythm right. They have to be an even match. There's a way to do naughty. You can do crass if you're witty at the same time." Are he and Kunis - this is the rumour - dating? He says not.
Most boy-band-types are like dandelion clocks: they look pretty for a while, only then the wind of fashion blows and they are scattered, gone forever. The lives of ex-child stars, meanwhile, famously tend to go into a downward spiral - which is what has happened to Timberlake's ex-girlfriend, Britney Spears, whom he met when he joined the cast of The Mickey Mouse Club in 1993 (they became a couple in 1999 and split up in 2002).
Timberlake, though, seems to be in possession of an almost super-human work ethic. His business interests alone - there are restaurants, a clothing line, a golf course, a vodka brand - would happily adorn the portfolio of a fat plutocrat three times his age. Was he always like this? Yes. Timberlake grew up in Shelby Forest, Tennessee, a smallish community near Memphis where his father was director of the choir at the local baptist church (his parents divorced in 1985, and his mother now runs Just-in Time Entertainment Inc).
Right from the start, it seems, he knew what he wanted to do. It was he who pushed to enter television's Star Search (he sang country music songs) and he who pushed to become a "mouseketeer" - and he isn't remotely embarrassed to say so. "If my parents hadn't got me to those auditions, at some point I would have found a way myself. It wasn't down to them. I remember my mother saying, 'I will take you to every audition, I will support you, but the minute you stop caring about it, I will stop'."
When he joined 'N Sync, he worked even harder. "I was the youngest in the group, but I also grew up being an athlete, and so you have this thing in the back of your mind that practice is important, that preparation is as important as performance. We used to do 'quick outs' - that's when you say goodnight, but the band keeps playing and the lights go out and you go right on to the bus and out of the venue to beat the traffic and get to the next city. They would tape the show for me with a right-angle camera and I would get on to the bus and watch it and make notes right off, then I'd give them to the lighting guys and the other members of the band. I was very serious. I was too serious, probably. It's very type-A [obsessive] behaviour, don't you think?"
And was this process helpful? "Well, I was never satisfied. I always had to be better." Didn't the others get sick of him? "Probably. I think we all cared about it, but on different levels. We were being pitted against all these other groups, it was this big competition. We thought 'we're better than them'. So we worked really hard. We had a lot of fun, too, on the road. But as a lifestyle, it's isolating, and weird, and sometimes really sad.
"It's manic. That's the best way I can describe it. You go from an arena of 80,000 people to a tour bus where you're all alone, from a place where the decibel level is so loud you can almost see it, to absolute silence. It's a manic experience."
He admits it took him a long time to get used to it. "You have to know what is real about your connection to it. Even though you might have written it, the song they [the fans] are singing is every bit as important as how they're looking at you." Even so, didn't this kind of adoration go to his head? "No, no. There's a level of performance that takes a lot of confidence, and sometimes that can be misinterpreted, that's all."
In the 90s, 'N Sync followed the lead of Backstreet Boys and sued their manager, Lou Pearlman, for fraud (Pearlman has since been sentenced to 25 years in prison for his part in a Ponzi scheme). The paranoia, I'm guessing, must have set in early on and it must be hard to find people he can trust. Timberlake snorts. "Yeah, well, I've been doing it long enough, haven't I? Your bullshit meter is tuned-in. You become adept at knowing what someone's intentions are." Casual encounters must inevitably be viewed through the filter of his public image. "It's always going to be a misunderstanding at first, good or bad. I can't control what impression people have of me, what little thing they have seen me do.
"Sometimes I used to break my neck to try and make people feel disarmed because I didn't like it that they were so nervous or excited around me. Other times, I would misinterpret that [behaviour], especially if there were cameras around. I'd think: this isn't real, and I would act up.
"There's a lot of acceptance [involved] ... there are always going to be people who have a connection with you that's not based on who you really are, but on what you do. Once you separate that out for yourself, you're more comfortable. What I do is a piece of who I am, but it's not all. I'm a son, at some point maybe I'll be a boyfriend again. I'm a friend, I'm a nephew, I'm a grandson. I'm all those things."
He has also been careful to stay in close touch with his school friends.
"Actually, I was just texting my best friend. He's in Montana. What makes most people comfortable is some sort of sense of nostalgia. I grew up in a small town and I could count my friends on one hand. I still live that way. I think I'll die in a small town. When I can't move my bones around a stage any more, you'll find me living in a place that's spread out and rural and spacious."
But what about the fortune he is so anxious to avoid discussing? Doesn't it distort everything?
"It's about good parenting," he says, earnestly.
"I got lucky. My stepdad is a banker, and he's really good with money. There was a point in my teenage years, when we were starting to play bigger shows and females were running after tour buses and all that, and my mother - and I remember this like it was yesterday - said, 'look, I want you to know that I couldn't be prouder of you. You are extraordinary. You move people. But it doesn't make you better than them. You still put your pants on the same way as them, one leg at a time, every morning'," He smiles.
"I thought about learning to jump right into them, just to mess with her. But what she said stuck with me, and I think it's true. I will just say that I am pretty frugal. I'll probably shop [for clothes] for myself once a year and that will last me for the rest of the year. What was it that Prince said? 'Money can't buy you happiness, but it can help pay for the pursuit.'
"It's nice to have places in LA and New York. I spend enough time in both that it's nice to have a home. But I don't need them. I always thought I'd fly on Southwest airlines, so this sounds crazy, but if I'm able to charter a jet, my friends are so grateful and so excited. None of them takes anything for granted, and I don't think they'd let me act that way, either."
Any minute now, the PR is going to knock on the door. I look at Timberlake and wonder if he is happy. Is he? For the first time, he looks mildly flustered. It's such a cheesy, obvious question and yet, it's as if I have asked him to drop his trousers.
"What, you mean, like, right now?" No, I mean in general. "Well, I don't feel discontented anymore, and I think I did before." He sort of cranks the words out. "I ... do ... feel happy. If I'm being honest about my cognitive nature, then I've had a lot of people tell me I was going to fail. A lot of people doubted me and I still have a sense of that, only now I feel differently about it. I no longer need to prove them wrong."
Are the next few movies stacked up, like planes coming in to land? "No. I don't have anything on my plate at all." So ... what? He's off to the beach? He laughs. "That is a little bit what I'm saying to myself. Go to the beach. One thing I've learned is, you do need to take time out here and there to ... enjoy life." His voice is at odds with his distressed jeans but it matches perfectly his tweedy flat cap.
Suddenly, he sounds so very old. "In my 20s, what I did was who I was. I don't feel that way any more. It's not about what you can put out in the world. I feel validated by things that aren't about expectation, either other people's or my own. True success is ... the process."
Friends With Benefits is at cinemas now.
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