At first glance, he is an unlikely rock 'n' roll star.
He might be 35, but he has the diffidence of an awkward teenager, while his open-necked white shirt, jeans and black blazer make him look more like a dressed-down City slicker than a hellraiser.
But there is something about the hooded eyes and cherubic face that is eerily familiar.
And when James McCartney takes to the stage in America's music capital, Nashville, he seems instantly at home under the spotlight.
The crowd has been queuing around the block to gain entry to The Bluebird Cafe, a legendary nightclub on the edge of town where stars such as Taylor Swift were discovered.
The venue seats just 100 people and competition for space is keen, even though most admit they are there out of curiosity.
"I want to see what the offspring of a Beatle looks like," one woman tells me as the lights dim. It also seems that many are expecting a Beatles-esque performance.
But James sounds nothing like his famous father, Paul, and at first the crowd are polite, but subdued.
However, as the show progresses they are won over by his musicianship, pure singing voice and quirky charm.
If his soulful, spiritual lyrics have something of The Beatles about them, they are more Harrison than Lennon and McCartney.
His encore is met by a rousing standing ovation. It's clear — even to his doubters — that James is a natural performer, almost as if the confidence and charisma of Paul have been handed down in the genes.
In person, the boyish James can look uncannily like his father, yet while Paul is garrulous, James is softly spoken and sensitive.
He fiddles anxiously with the pendant hanging around his neck, and toys with a silver Navajo bracelet on his wrist and a gold trinity ring — a gift from his parents — on his finger.
This is his first ever in-depth interview and it's clear that he's looking forward to it like a trip to the dentist. But though talking about his background is difficult, James is honest and likeable, and looks me straight in the eye while he speaks about the advantages and difficulties of growing up in one of the most famous — and wealthiest — families in the world.
"I'm naturally guarded because of the way I was brought up," he tells me. "But I understand people are interested in who I am. To me, it's all about the music. Having said that I want people to know who I really am — I'm OK with the truth."
He discusses his father's disastrous marriage to Heather Mills ("I didn't like her"), the pain of losing his mother Linda, and how he "lost" most of his 20s in a haze of drugs — a downward spiral that ended in rehab and caused a rift with his father.
Though his accent is softly modulated English, he peppers his conversation with Americanisms such as "awesome", which are clearly a throwback to his American mother and perhaps the influence of his father's third wife, New York heiress Nancy Shevell. James says he "adores" Nancy and considers her his "new mother".
Though he has played guitar since childhood, it's only now that James has decided to follow his father into the music business, a prospect he describes as simultaneously "thrilling and a bit nerve-racking". It's not difficult to guess why it's taken him so long to pluck up the courage.
"It's hard to live up to The Beatles," admits James. "When Wings toured they got slated. Even Dad found it hard living up to The Beatles. I started out playing under an alias because I wanted to start quietly.
I had to serve my time as a musician and wait until I had a good body of songs and for a time when both myself and my music were ready. I don't want to sit around. I want to earn my own living."
He certainly hasn't been sitting around.
In a marathon schedule that echoes the tough training The Beatles endured in the nightclubs of Hamburg at the start of their career, James is now nearing the end of a 47-date, 27-state American tour.
Travelling in a white minivan, James and his tiny entourage (his manager, tour manager and bodyguard) have driven more than 13,000 miles, staying at cheap motels (a cockroach skitters across the floor of the one where we meet).
James plays "hole-in-the-wall" venues, often to just a handful of people.
The aim is to introduce him to the US market and showcase his first solo album, Me.
"It is about the music and keeping it authentic. I don't need a huge entourage. It's cheaper to drive than fly so we go around in a minivan.
"We don't need to stay in five-star hotels. It makes sense to do it this way. I want to earn people's respect."
On stage he is self-deprecating — "This is one I wrote with my dad.
You might have heard of him."
But the only cover version in his repertoire is Neil Young's "Old Man" (the lyrics include "Old Man look at my life, I'm a lot like you were") which gets a big response.
A young James with Paul and Linda
"Growing up, I put a lot of pressure on myself," he explains. "I felt with The Beatles legacy that there was pressure on me to do music, and while I always loved music and it was always around me at home, I thought about doing other things. I did art, I made furniture. I didn't want to be a cliche — the Beatle's son who became a musician."
Like his sisters, James went to state-run Thomas Peacocke school in Rye, East Sussex, near the family's 160-acre farm. Summer holidays were spent in Scotland at a place made famous by one of Paul's biggest hits, "Mull Of Kintyre."
"It was a lovely childhood. I was shy but enjoyed school. I was protected by my family," he says.
"I understand people want to know more about me, but it's hard to know how much to divulge of my personal life. I've never talked like this before. I wouldn't want my dad to be upset. I don't want to weird him out."
Was he aware, as a child, that his dad was "different"?
"Yes, of course. I was treated normally at school, but there was always stuff going on when we went out. Plus there were the people who came to visit." He pauses before listing a string of household names who would regularly turn up at the family farm at Peasmarsh — George, Ringo, Paul Simon, Carl Perkins.
"To me they were just Mum and Dad's friends but I knew not everyone had a dad who was a Beatle."
But there's another reason, too, that James has taken so long to blossom. His "perfect world" was turned upside down when the mother he adored was diagnosed with incurable breast cancer.
"When I was 17 I wrote my first song and then Mum was diagnosed with cancer. She died when I was 20 and that's when I went into a very dark period.
"I was studying art, photography and English at college. I had spent a lot of time at home with Mum and Dad. I got a bit of flak from the college because I wasn't really present, but I never regretted spending that time with her."
|James McCartney's album, Me, is available at Amazon.
Speaking of rumours he had slept in a bed with his father for "months" after her death, he told the newspaper: "We were both grieving together.
"That first night, in Arizona, when she'd just died I thought it would be too sad for Dad to sleep on his own so I kept him company."
James smoked his first marijuana joint at 16, but says the death of his mother "devastated" him and led him to seek solace in drugs and alcohol. He is now "several months sober" and has "re-bonded" with his family after drifting apart.
McCartney has a new album, entitled Me, and is currently touring the US.
He has previously disclosed he would consider forming a "next generation" Beatles with the offspring of other band members, saying: "I'd be up for it. Sean [Lennon] seemed to be into it, Dhani [Harrison] seemed to be into it. I'd be happy to do it."
Article first published in The Daily Mail, June 15, 2013. Some portions added or abridged.