James Whitaker: Journalist who became the most respected of royal correspondents

James Whitaker's good fortune was to be appointed Royal Correspondent of the Daily Mirror at the beginning of two decades when the doings of the royal family became almost a national obsession, with as many scandalous and improbable twists and turns as an overwritten television soap opera. It was a time, too, when the notions of discretion and subservience that had formerly restrained the press from delving too intrusively into the lives of the royals had been cast aside. Almost any titbit offered by a person connected with the court could be crafted into a story which could not, by convention, be denied by those said to have been involved in it.

Even if he did not set out on the road to Fleet Street with the settled ambition of covering the royals, it was the direction in which his career path would take him from quite an early stage; and he was alert enough to recognise it as a specialisation that suited him admirably. Although he was described in 1996 by the media academic Jeremy Tunstall as "the father of aggressive royal reporting", his manner was the very opposite of aggressive. Affable, clubbable, with a plummy, booming voice and a rotund figure, he was able to gain the confidence of the young royals and members of their circle, while keeping under wraps the ruthless streak that was an essential tool of his trade.

"I had contacts at all levels built up over the years," he told The Guardian in 2006, "from the people who swept up the shit from the Queen's horses to astonishingly senior people who worked for the royal family. I never, ever, paid my best contacts, you could never offer them money, although I sent them the occasional case of very good claret."

He stood down from full-time engagement with the royals not long before the phone hacking and bribery scandals and the ongoing Leveson inquiry, which together have already induced the tabloids to adopt a more cautious approach. The salad days of royal reporting are unlikely to recur.

Born in Cheltenham in 1940, and educated at Cheltenham College, he made a false start in accountancy before joining the Hounslow, Brentford and Chiswick Post as a reporter. In 1967 he was recruited to the Diary column of the Daily Mail where, he said later, he acquired a taste for attending royal events – and especially for the champagne and smoked salmon sometimes served at them. Other aspects of the royal lifestyle – including horse racing and field sports – also appealed to him.

He quickly made a name for himself as a talented gossip writer and was recruited successively by the Daily Express, The Sun and the Daily Star, where for the first time he was given the title of Royal Reporter. In 1983 he took up the same job at the Daily Mirror, where he worked for 20 years.

More than most of his rivals, he liked to insert himself into his stories, constructing an image of a man on intimate terms with the people he was writing about. In March 1990, when he went to Nigeria to cover the visit of Diana, Princess of Wales, he confided to his readers: "In 1980 when she first became talked about as Prince Charles's wife, I would tell her that this marriage must happen. 'Why?' she would say, 'What's so special about me. Why would I be suitable?' I would tell her that there were a million reasons why she should become the Princess of Wales, not the least of which was that she was unutterably charming and that everyone loved her for her freshness and naiveté."

His two most vaunted scoops were also about Princess Diana. He revealed that she suffered from anorexia – an allegation vigorously denied at the time by the Buckingham Palace press office, but later acknowledged to be accurate. In 1998, after Diana's separation from Charles, he discovered that she was having an affair with Dodi Fayed, which earned him an award for the Scoop of the Year. Such stories do not, clearly, place him in the ranks of the titans of investigative journalism: but within his own field he was rightly admired by his peers and rivals.

The high point of the age of royal reporting came, naturally enough, at the low point in the Queen's 60-year reign – in 1992, the year that she described as her annus horribilis. "In 25 years as a royal reporter I have never known anything like it," Whitaker wrote in the Mirror. Among the stories he was called upon to report were the separation of Charles and Diana and of the Duke and Duchess of York, the "squidgy tapes" recording telephone conversations between Diana and James Gilbey and the disastrous fire at Windsor Castle.

The following year he wrote a book, Diana v. Charles, including transcripts of monitored telephone conversations between the two protagonists. The Mirror's publication of extracts from the book was referred to the Press Complaints Commission. He left the Mirror in 2003 but continued to comment on the affairs of the royal family as a freelance on television and radio, as well as in print.

Inevitably, though, some of his scoops turned out wrong. In 2007, in the early days of the long courtship of the Duke and Duchess of Cambridge, he toldThe Independent: "I do believe I am the only journalist to this day who knew William and Kate Middleton would never marry."

His final encounter with the Queen came last November, when he attended a reception for journalists to mark the eve of her Diamond Jubilee year. By then he had been diagnosed with a virulent form of cancer from which, despite several operations and treatments, he died yesterday. He is survived by his wife Iwona and three children, Edward, Thomas and Victoria.

Michael Leapman

James Whitaker, journalist: born Cheltenham 4 October 1940; married Iwona (three sons); died 15 February 2012.