Perhaps the most impressive thing about Tina Brown’s new biography of her apparent longtime girl crush, the doomed Princess of Wales, is that one doesn’t feel totally embarrassed reading it.

To some extent this is a feat of packaging. The book is meticulously endnoted and indexed. There are no photographs, save for a restrained black-and-white collage of Iconic Diana Moments spread across the endpapers, and a Vaseline-lensed Annie Leibovitz color portrait of Ms. Brown, in minimalist crisp shirt and pearl stud earrings, hand thoughtfully propping up cheek, on the back. The author’s name appears in sober, royal-purple capital letters, set against a vanilla background; her subject’s in a raised, Eloise at the Plaza–pink script, like icing on a birthday cake. Cosmetically at least, Ms. Brown’s latest Topic A, which has a bit of an irrelevant, fin-de-millénium feeling—rather like Ms. Brown herself—has been sufficiently freshened. But what about the substance?

It will be 10 years ago this August that New Yorkers awoke, somewhat quaintly in retrospect, to dramatic front-page newspaper reports that Princess Diana had perished alongside her then-boyfriend, Dodi al-Fayed, in a car accident in Paris. Their driver was measurably intoxicated, but because his passengers had been pursued by what Ms. Brown disdainfully terms “the farting motorbikes of the international press” (later she calls them “the furies”), the incident provoked one of those unbearable and completely ineffectual media mea culpa marathons, with earnest panels on CNN, George Clooney’s head bobbing indignantly in frame, etc.

Since then, the paparazzi have only grown more vigorous (see Us Weekly, TMZ.com and the like). The monarchy is another matter. To assess how far they’ve fallen in public esteem, one need only compare Stanley Donen’s 1951 movie musical Royal Wedding, in which the nuptials of Queen Elizabeth and Prince Philip were but a respectful backdrop, to Stephen Frears’ high-beam 2006 biopic The Queen, which—let’s admit it—would’ve been entirely appropriate programming for the Lifetime channel, despite the accolades for its star (a dame of the British Empire) from the notoriously Anglophiliac Academy of Motion Picture Arts and Sciences.

The reality TV show careers of Paul Burrell, Diana’s butler of betrayal, and James Hewitt, her cavalry man turned chatty lover, suggest further that the entire apparatus supporting the royal family—or as Ms. Brown is fond of calling it, The Firm—might some day crumble under the giant wrecking ball of cheap fame. Even since—especially since—Prince Charles and his longtime mistress Camilla Parker Bowles married and settled into a comfortable, quiet life of unleashing the hounds, eating kippers, striding the moors and whatever else it is upper-crust Brits do, the principals have seemed decidedly vestigial, out-of-touch, superfluous: museum pieces, under glass.

Diana was different, as Ms. Brown tells us—not for the first time, God knows, but with a certain metropolitan elegance and assertiveness that manages to make the story seem passably absorbing again. Diana was noisy: bopping around listening to pop tunes on her Walkman; giggling with Sarah Ferguson, former Duchess of York, the lesser casualty of the famous Windsor hauteur; or barfing up her frequent food binges (Ms. Brown lingers with peculiar savor on this topic, pointing out how “Buckingham Palace was tailor-made for a bulimic outburst. It is suffocating and empty at the same time,” and deeming Balmoral, the royal retreat, a “dank vomitorium”). Diana was touchy-feely: affectionate toward her two young sons in public, sympathetic to orphans and AIDS patients and victims of land-mine explosions. Diana could also be a little bit trashy—hey, kind of like Tina Brown at The New Yorker, that monarch of magazines, which many felt was becoming an out-of-touch museum piece until she ruffled up its pages.

Also, Diana was pretty, though many a little girl, woken up early to watch her walk down the aisle, wondered why this so-called princess didn’t grow her golden hair long, like they do in the storybooks. Indeed, author and subject were eerie partners in coif for many years, and Ms. Brown is still working a variation of the cropped, feathery, frosted do, perhaps in memoriam. Repeatedly she pays tribute to Diana’s terrific gams, fine teeth, great skin. “Softer than a child’s velveteen rabbit,” Tina croons about that English-rose complexion, which she appears to have all but stroked at a Four Seasons luncheon with Vogue’s Anna Wintour, not long before Di’s death. “No wonder she made such an impact at the bedsides of sick children.”

This is the essence of what Tina Brown brings to the groaning table of literature on Diana, Princess of Wales: the presence of Tina Brown, editor in chief. Here she is during her New Yorker stint, sitting near a knuckle-cracking Charles at a performance of the Royal Shakespeare Company in Cerritos, Calif.—the perfect T.B. meeting of high and low. (“They’re strange, aren’t they, in L.A.?” the Prince mused endearingly. “I mean, they all want to go to bed at 9.”) Here she is summoning outtakes from a long-ago Tatler photo shoot she supervised at the Parker Bowles’ home: Camilla’s husband Andrew, Tina reports, “spent the whole shoot staring at my chest.” (So Di isn’t the only one with delicious décolletage.) Here she is braving the harsh reaction from The Daily Mail (“How Would Tina and Harry’s Marriage Stand Up to the Vanity Fair Treatment?”) to her gossipy VF story about the royals.

But despite these glory days, it’s actually the mantle of the failed Talk magazine that clings most tenaciously to Ms. Brown—there may be no references to “the conversation” and “the buzz” in The Diana Chronicles, but there is one to “Diana synergy.” Somehow providing sporadic analyses of phenomena like the “bewilderingly promiscuous” British press and the “gossip industry” grants her license to hold herself aloof from the Fleet Streeters of this world—the Andrew Mortons, Kitty Kelleys and Martin Bashirs—even as she relies heavily on their reportage and their methods. At one point, Ms. Brown, who herself makes liberal use of anonymous sources, compares Mr. Morton, who was practically Di’s official confidant, to Bob Woodward.

Tina has people like John Travolta pop in for on-the-record chitchats, lest we forgot for a moment that she still has the potentates of P.M.K. on her speed dial. And the material she gathered from nameless sources clearly required no sordid assignations in darkened parking garages. She was well taken care of on her research trips to London: Ian Schrager made a room available for her every time she hit town “at his fabulous Sanderson Hotel in Berners Street,” Ms. Brown boasts in her acknowledgements. God forbid she should stay at a Hilton.

Alexandra Jacobs is editor at large at The Observer.