Sex is the last refuge of the miserable, said Quentin Crisp, but for Sir Dai Llewellyn it was his glittering prize for winning “the lottery of life”. For decades the Welsh “seducer of the valleys” seemed intent on giving philanderers a bad name, such was his appetite for wine, women and song. At parties he was always the last man standing; now the bill has brought him to his knees.

Cirrhosis of the liver and cancer may have confined the 62-year-old boulevardier to a hospice in Kent, but Llewellyn still relishes a defiant glass of wine a day. There is comfort, too, in his recent reconciliation with Roddy, his younger brother, after a 30-year estrangement triggered by Dai’s indiscretions over Roddy’s affair with Princess Margaret.

The loss of five stone has reduced Llewellyn’s Falstaffian rotundity to a pale semblance of his younger self, when the handsome, rakish Old Etonian was the toast of the best parties. He let himself go, he once said, because of his aversion to gyms: “I can’t bear the smell of other men’s feet.”

Not that the fourth baronet of Bwllfa was short of exercise. On one occasion in 2005, he slipped off with another man’s date and they had just got comfortable when “the corner of the bed started to go. We plunged through the floorboards and a wardrobe fell on top of us”, he recalled. His companion braced her legs against the cupboard doors while he hauled them to safety. “I’d wanted her legs in the air, but not quite in the same way.”

He was fond of saying that he never got up in the morning planning to make love to three women, “but if it happened, it happened”. According to his friend Paul Callan, the journalist, Llewellyn was not exaggerating: “He told me about a hilarious episode of having three debs in a bed, each of whom he was happily servicing, while a Mexican band stood naked around the bed serenading them.”

It was Callan, then working for the Daily Mirror, who caused animosity between the Llewellyn brothers in 1976 by reporting Dai’s revelation that Roddy was bisexual. “It was the first time it had been printed,” said Callan. “I think Dai was also bandying stories around Fleet Street about Roddy and Princess Margaret.” Llewellyn himself had become a gossip writer’s favourite thanks largely to the late Nigel Dempster, the Daily Mail gossip columnist and a close friend. Roddy, a landscape gardener, said he had never forgiven his brother’s “abhorrent” account of the royal romance, much of it conducted in Mustique.

After a series of spats, the brothers had not spoken since 2006, when Dai banned Roddy from his proposed wedding to Christel Jurgenson, a Swedish-born interior designer, for whom he renounced his wicked ways. Despite their shared love of smoking, drinking and staying up late, she dumped him and the marriage never took place.

After the brothers’ reunion at a pub near the hospice, Dai declared that blood was “thicker than wine” and that “the hatchet has been buried for ever”. They would never fall out again, he swore: “I love my brother. We are friends and will be to the grave.”

It was the drink that brought about his downfall, Dai admitted in a recent interview, while simultaneously extolling the joys of alcohol. One night, he boasted, he drank eight bottles of wine, one bottle of vodka, a bottle of rum and a bottle of port. “At 6am I was totally lucid.”

Callan can vouch for Llewellyn’s prodigious thirst: “He really went at it. I spent a week with him to get his story and, when I came back, I had to take a rest for a couple of days.” Yet beneath Dirty Dai’s licentious mask, the journalist glimpsed a sensitive soul: “I don’t think there’s a malicious bone in his body. He’s a sort of decadent Bertie Wooster – not tremendously bright but well intentioned. There was kindness there.”

Nicky Haslam, the interior designer and writer, got to know Llewellyn in the mid1970s, inviting him to lunch at his studio and staying at the playboy’s rundown farmhouse in Wales. “When I first met Dai he was incredibly good-looking and well dressed. The girls fell for him like mad.”

Llewellyn’s pulling technique appears to confirm the theory that women like rascals who can make them laugh. His own explanation uncannily echoed Casanova’s: “I gave the message that I loved everything about women – smell, make-up, jewellery, the whole f****** shebang.”

However, the bon viveur caused outrage in 1992 by claiming that women were “over the hill” at 30 and recounting that he had once seduced a 17-year-old with “the body of a pubescent gazelle” only to discover she was 15.

Llewellyn’s interest in the opposite sex came as a pleasant surprise to his parents. “When I was in my teens I was quite a pretty boy and I think my parents thought I was going to turn into a pansy,” he recalled. “I was a very late developer – all the Llewellyns are – and everybody was frightfully worried I was going to turn out limp-wristed.”

Born on April 2, 1946, he was the eldest son of Sir Harry, the third baronet, whose father had bought the title from Lloyd George (Harry succeeded after the death of his elder brother, Rhys, the second baronet). Although Sir Harry was a national hero who had been separately knighted after winning a gold medal for show-jumping in the 1952 Olympics, he presented a daunting figure to Dai, Roddy and their sister Anna. “As a child I was quite frightened of Pa. I loved him, but he could be fearsome.”

The siblings doted on their mother, Christine, the daughter of the 5th baron de Saumarez and a descendant of Admiral James Saumarez, who was second-in-command to Nelson at the battle of the Nile.

After an early childhood at Gobion Manor, near Abergavenny, Dai was sent to prep school at Hawtrey’s and from there to Eton. Deciding he had “had enough of rules”, he chose to continue his studies at Aix-en-Provence.

It was in the south of France in the 1960s that he began a lifelong friendship with Taki Theodoracopulos, the Greek shipping heir and High Life columnist in The Spectator.

“Dai was chasing p****, like I was,” Taki recalled. “He had a line with girls that I gave him: ‘Would you like to be the future Lady Llewellyn?’ We had a lot of fun. He would always come to my parties. We used to have dinner once a week at Aspinall’s [the exclusive London gaming club]. Dai wasn’t a big gambler: he was always short of money, yet he always went first class. He didn’t have the kind of money other people had, but I never saw him as a hanger-on. He had his pride.”

In 1967 Llewellyn set off around the world to make his fortune, initially as a male model named David Savage. He returned two years later to find that the girl he had planned to marry, Lady Charlotte Anne Curzon, had gone off with another man. After a few years as a travel agent, he was recruited by Victor Lownes, the Playboy executive and owner of the Clermont club, as social secretary.

His engagement in 1975 to Isabel Richli – whom he called “Isabel Very-Richli” – foundered when he ventured into Tramp nightclub one evening and experienced a “coup de foudre” on seeing a striking girl in a red dress. This was Beatrice Welles, daughter of Orson, the actor-director. “It was a marvellous time,” he said. “The only trouble was we fought like cat and dog.” She once knocked him unconscious while he was driving on the motorway and he called time by emptying a glass of brandy over her head.

Eventually, in 1980, he married Vanessa Hubbard, niece of the Duke of Norfolk. “I was a much better husband than people think,” he maintained. The marriage lasted seven years and produced two daughters, Olivia, now a 28-year-old actress, and Arabella, a 25-year-old banker. After his divorce he took up with Annegret Tree, a renowned beauty of the 1960s, and then Judith Wilcox, who was to become Baroness Wilcox of Plymouth.

On becoming the fourth baronet after his father’s death in 1999, Llewellyn employed his talents in opening clubs and organising events around the world. In 2002, while “slightly tipsy”, he bought six houses in Monmouthshire, but was wounded when vandals gutted and torched them.

These days he feels like a character from The Bonfire of the Vanities: “I was king of the world. I was invincible, above the rules of society. Except I wasn’t, and it damned near killed me.”

He had been feeling ill for years, but overlooked the warning signs until he collapsed in June and was taken to hospital in Tunbridge Wells. Prostate cancer has spread to other parts of his body. “I’m riddled with it,” he told the Daily Mail last weekend. “I have been told I can’t be cured, but I can get better. No regrets though, “I won the lottery of life: being born British, being an Old Etonian”, and a healthy realism: “There’s no difference between a washed-out bum on the Embankment and a champagne Charlie rotting his liver to death.”

People view a playboy’s life as a useless occupation, but Llewellyn is not so sure. Society needs someone to be the life and soul of the party, he believes. “And at least I was the best at what I did.”