Gary Goldsmith – the Princess of Wales’s naughty uncle and self-styled King Of Fun – is telling me about his ‘wholesome and civilised’ 60th birthday celebrations at his Ibiza villa.

He’d enjoyed a few alcohol-free beers over lazy lunches with friends, taken the odd dip in the pool, played tennis and gone hiking. And, yes, you read that correctly. The party animal hadn’t touched a drop of alcohol.

The only concession to self-indulgence was his birthday meal – a feast of seafood and cake. The newly abstemious Gary had not only turned his back on alcohol, he’d also been on a quest to lose weight.

Gary had jumped on the Mounjaro bandwagon and been using weight-loss jabs for the past year and lost 6st. So allowing himself a well-deserved pause in his strict regime had been the highlight of his birthday week.

Then, eight days after his birthday in April last year, the younger brother of Carole Middleton, mother of our future Queen, had a brush with death. ‘I’d fallen asleep on the sofa watching rubbish box sets,’ he recalls. ‘And when I woke up around 7am, still on the sofa, I started feeling terribly sick. I managed to stagger to the loo, where I was projectile vomiting blood. It seemed to go on for hours.’

Gary Goldsmith – the Princess of Wales’s naughty uncle and self-styled King Of Fun – has jumped on the Mounjaro bandwagon and lost 6st using weight-loss jabs over the past year

The health emergency that followed marks the latest humbling chapter in Gary’s colourful life – and it is one which has made him all the more appreciative of the indomitable Middleton spirit, and the love of his no-nonsense big sister Carole. ‘I hate fuss and I hate being told what to do,’ he tells me, as he recalls that frightening episode.

Nevertheless he did call Julie-Ann, 56, his wife, who was at home in London looking after their dogs, to inquire if she thought he really needed to go to hospital. She said he did and swiftly bypassed her husband completely, ringing Gino, his house manager in Ibiza, who drove him to the island’s private hospital.

Within 12 crucial minutes, he was rushed through triage for life-saving surgery in which bands were tied around the veins in his oesophagus which had become enlarged as a consequence of liver disease and were threatening to burst. ‘If they hadn’t banded me I would have bled to death,’ says Gary, who spent the next 48 hours in intensive care.

‘There were people dying all around me. I find hospitals horrific so I checked out and went home. The doctors were pleading with me to stay. Gino was in tears. He rang Tallulah [Gary’s only child, from his second marriage to Luan Bettaney] who was absolutely furious with me.’

His wife and Tallulah, 24, who had by then flown out to be with Gary, could not persuade him to return to the island’s hospital. Weak but typically intransigent, he flatly refused. Tallulah gave him a stern talking to. If he would not go back to the Spanish hospital, she said, he must fly immediately to London for treatment.

‘She insisted I grow up, go home and start taking my health seriously. She said: “You need to change some stuff and look after yourself more. You’re 60 not 16.”’

Gary, seen prior to his weight loss, attends Pippa Middleton's wedding with daughter Tallulah

Tallulah also set about contacting family and friends, urging them to talk some sense into her father. Crucially, one of those was his big sister Carole, 71.

‘Tallulah texted her to tell her how ill I was. She weighed in, wanting me to be more mindful of my age, to make sure I was getting enough sleep, eat more healthily, do more walking, stay active, drink less and take supplements.

‘As she is ten years older than me, when we were kids, it was like growing up with two mums. She still has that maternal concern for me. We were raised in a really modest little house in Southall, Middlesex, and family meant everything to us. We looked out for each other.

‘If I did something wrong, I got told off twice, once by Mum and then again by my sister.’

It is a combination of all these qualities – familial closeness, big-sisterly sternness and a steely stoicism – that still fires Carole today. It was typical of her that she endured privately and with dignity the cancer diagnosis of her eldest daughter. The news that Kate was in remission came just four months before Gary’s own health crisis.

During his treatment and recovery, he had time to reflect on his niece’s illness and appreciate that, in the midst of his sister’s worries, Carole had made time for him, too. ‘I’m very conscious that your brother being poorly is one thing. Your daughter, suffering with cancer is massive,’ he says.

The way Kate has dealt with her illness – serenely and without fuss – has left Gary ‘awestruck’

The way Kate has dealt with her illness – serenely and without fuss – has left Gary ‘awestruck’. He was ‘thrilled’ to see her take on the physically demanding Three Peaks challenge last month to raise money for London’s Royal Marsden Hospital where she was treated, proving – quietly and without fanfare – that she has recovered her fitness.

After scaling Ben Nevis in Scotland, Scafell Pike in England and Snowdon in Wales, in 24 hours, Kate posted a photo of herself at the top of Nevis, describing the challenge as ‘a chance to explore life beyond diagnosis and to give something back’.

Gary smiles. ‘It takes me back to her childhood when they would go to the Lakes,’ he says. ‘You put on your walking boots and off you go. For Kate, it felt like a return to nature, a return to her childhood.’

I meet Gary at a private members’ club in Marylebone, west London. It’s hard to equate this ebullient figure with a man who, little more than a year ago, so narrowly escaped death.

As he sips his alcohol-free lager, I spot a telling tattoo on his finger. It reads ‘sin alcohol’ which, he says, is a reminder not to drink.

Gary made his fortune in the recruitment industry, selling his shares in the company Computer Futures in 2005 for £17million.

‘My friends and I were probably drinking more than the average person because my business demanded a lot of entertaining,’ he says. ‘You just don’t expect your lifestyle to come back and bite you.’

When he returned from Ibiza he was taken to University College Hospital, London, for tests. Then came referrals to liver specialists. He concedes now that his illness must be the result of 40 years of excess. ‘My body just said: “No. You’ve had enough.” They’re managing my bloods every few weeks. But I’m fitter than I’ve ever been.’

The realisation that death had loomed close also affected his mental health. ‘I went into a dark hole,’ he admits. ‘I couldn’t sleep. I wouldn’t speak to anyone. I was bitter, twisted and scared trying to figure it all out. My emotions were just welling up and I couldn’t focus on anything.’

After seeing a therapist, Gary began to sleep more easily. He also realised that his salvation lay in ‘getting stuck into a project’.

One night, he woke up with an idea for a children’s book, based on stories he used to make up for Tallulah. The book, 26 Perfectly Imperfect Tales From The Village Of Mishaven, follows a series of characters who are ‘perfectly imperfect’. ‘I think the book has a really cool message for kids – every person has flaws but they are brilliant the way they are.’

So, what are his plans? ‘I want five grandchildren. Tallulah doesn’t even know that yet. I would like to have a five-a-side football team.’

With Uncle Gary’s penchant for reinvention, you’d be mad to bet against him.

You can buy Gary’s book at shop.ingramspark.com