Terry Keane, the mistress of the former Taoiseach Charles Haughey, created a sensation in May 1999 when she went on Irish television giving details of their affair, which had gone on for 27 years and had long been the subject of speculation, much of it fanned by herself. She followed on with extracts from a forthcoming book in The Sunday Times containing rather intimate photographs for which she received £50,000. The book never appeared.

Born Ann Therese O’Donnell in Guildford, Surrey, in 1939, she was the only child of elderly parents, both of whom came from Ireland. Her father was one of many Irish doctors who then practised their profession in Britain. When, in 1958, she completed her schooling with the nuns at Poles Convent in Ware, Hertfordshire, she went to Trinity College Dublin to read medicine.

A sultry beauty, she was soon distracted by the glamorous social life of the college, many of whose students were public school English trying, in her words, to re-create Brideshead in the middle of Dublin. Within a year she had departed the college but remained in Dublin writing for a society magazine and doing part-time modelling.

She fell in love with Ronan Keane, then a rising young barrister, and they planned to get married as soon as he could afford it. However, in the aftermath of a tiff, she had a one-night stand with an actor, Jimmy Donnelly, and became pregnant. She retreated to England and the child, a daughter, was born.

Ronan Keane remained willing to marry her but, on her account, insisted that she should give away the child for adoption. She did this unwillingly and they were married in the closing days of 1962. They soon had three children of their own.

Terry Keane was not prepared to follow the example of most Irish wives of the period and abandon her career to look after her home and children. She was employed by The Irish Times to write a column on fashion and enjoyed the social whirl while her husband worked day and night on his briefs.

Her marriage was in difficulties when in 1972 at a party in a nightclub she met Charles Haughey, then in the political wilderness, having been dismissed from the Government two years earlier on suspicion of complicity in the illegal importation of arms for use in Northern Ireland. He invited her to travel with him to London the next day and their affair began.

Her marriage staggered on. It was some ten years before she and her husband finally parted and they never divorced even after divorce became available in Ireland in 1996. There were legal proceedings that were settled leaving her in possession of the family home. Haughey, for his part, never seems to have contemplated leaving his wife.

Although he was by no means the only man to enjoy Terry Keane’s favours, Haughey became the chief love of her life. He lavished gifts and entertainment on her, apparently captivated by her patrician tones and the lofty disdain with which she treated him, describing him to his face during her periodic tantrums as a common little man. They shared an interest in art and literature, of which she was a good judge.

The affair remained out of the public domain because it was the firm practice of Irish newspapers not to expose the private lives of politicians. There were reports in British publications such as Private Eye, but these were dismissed by Haughey’s followers as malicious attacks of a kind that the English could be relied upon to make against patriotic Irishmen.

Keane turned her connection to advantage in her journalistic career when she was recruited in 1989 by the Sunday Independent to write a gossip column called the Keane Edge, which was full of veiled references to her relationship with Haughey, usually described as “Sweetie”. It enjoyed a good readership and was often very clever.

By 1999 Haughey, who had ceased to be Taoiseach in 1992, was beset by tribunals of inquiry into gifts he had received while in office. He had also been given a diagnosis of prostate cancer. He invited Keane to lunch at their accustomed venue in the Coq Hardi restaurant in Dublin. Announcing that he was trying to get his life in order he returned photographs and mementoes that she had given him.

Stung by Haughey’s insensitivity and strapped for cash (another of her paramours had persuaded her to become a name at Lloyd’s with disastrous consequences), she decided to sell her story to The Sunday Times and appeared on television to advertise its imminent publication.

Haughey was not the only person to be upset by her memoirs. She accused an elderly priest of having had an affair with her when she was living at home in England, a charge hotly denied. She boasted that through Haughey she had secured her husband’s appointment as a judge, an allegation that could have been unhelpful at a time when his appointment as Chief Justice was in the offing.

At first she was unapologetic about what she had done. “Like St Augustine” she announced, “I believe that my real life has begun since my confession.” When Haughey refused to see her again she sold at public auction his portrait, which he had given her, and a bust of herself that he had commissioned.

As part of the deal for the serialisation of her memoirs, she was employed to write a column in the Irish edition of The Sunday Times. In 2002 the newspaper was sued successfully for libel on account of an article of hers that was held to carry the implication that a fellow journalist, John Waters, was a bad father to a child he had had by the pop singer Sinéad O’Connor.

In 2004 Keane’s only son, Timothy, 39, who lived alone, was found dead in his Dublin flat. Then Keane was told that she had cancer. In 2006, six months before Haughey died, she went on television to express regret for the hurt she had caused his family and hers. This did not prevent her from selling a further instalment of memoirs for publication after Haughey’s death.

Keane was a generous, intelligent and amusing, if sometimes outrageous and tempestuous, person who retained the affection of friends and especially her family, including the daughter she had given up for adoption and with whom she was later reunited. She even persuaded her estranged husband, with whom she remained on good terms, to give the girl away when she got married.

She is survived by her husband and by her three daughters.

Terry Keane, journalist, was born in September, 1939. She died on May 31, 2008, aged 68