LONDON >> Poor Kate Middleton. She’s not just marrying a future king. She’s marrying all of us.

Once upon a time, British subjects gazed upon their sovereigns from afar. Not any more.

Members of the royal family are now Hollywood-style mega-celebrities — their cellulite, receding hairlines and boozy nights out subject to the same relentless scrutiny as other A-listers.

The monarchy has gained in star power, and perhaps lost in dignity, since William’s mother, Princess Diana, burst into the royal family in a blonde blaze of charisma and changed it forever.

On British newsstands ahead of Friday’s wedding, Kate and William beam from the covers of celebrity magazines alongside Catherine Zeta-Jones, singer Cheryl Cole and surgically altered glamour model Katie Price. One promises the inside scoop on “Royal Wedding Meltdowns!” Another says that “Pals Fear for Skinny Kate.” The royal couple is even on the cover of TV Times — the wedding will be the television event of the year.

It’s easy to forget that it was not always like this.

“When I was growing up I thought the royal family was harmless but a bit boring,” said novelist Monica Ali, whose new book, “Untold Story,” imagines an alternate future for Princess Diana.

“It was really when Diana came on the scene that things started to change,” Ali said. “She divided opinion. A lot of people adored her, some people didn’t like her, but everybody had an opinion about her.

“She brought celebrity into it — for good or for ill.”

“Untold Story,” out now in Britain and published in the United States in June, imagines that Diana didn’t die in a 1997 car crash, but faked her own death, changed her name and rebuilt her life in a small American town.

Ali, whose books include the best-selling London immigrant saga “Brick Lane,” uses the novel to muse on the price of celebrity and the pressures of fame.

“Kate is not just marrying into the royal family,” Ali said. “She is marrying into celebrity. She is entering the game show of the first wives’ club. She’ll be competing with Michelle Obama and Carla Bruni.”

There’s nothing new in a popular desire to read about celebrities, but over the decades our relationship with them has been transformed.

Perhaps it was the rise of the paparazzi, with their long lenses and lack of boundaries. Maybe it was the lowering of social barriers and inhibitions that began in the 1960s. Nowadays, we want to know everything.

Ellis Cashmore, a cultural studies professor at England’s Staffordshire University and author of the book “Celebrity Culture,” said Princess Diana was a key figure in this transition — and so, even earlier, was the late Elizabeth Taylor, with her emotional exuberance and health problems and turbulent love life.

“It wasn’t the Liz Taylor we saw in the movies we were interested in — we wanted to know the real person,” he said. “We became much more interested in people’s private lives — or what was once their private lives.”

The royal family remained largely off-limits — until Diana worked her fairy-tale magic.

The romantic 1981 wedding of Prince Charles and 20-year-old Lady Diana Spencer was followed by two sons, William and Harry. Then came bulimia, a suicide attempt and marital discord that was obvious to the world even before Diana told a TV interviewer in 1995 that “there were three of us” in the marriage — Diana, Charles and his paramour Camilla Parker-Bowles.

Throughout it all, paparazzi trailed Diana wherever she went. Her combination of glamour, personal warmth, charity work and unhappiness was gold dust.

“The humanizing touch Diana gave it was like a magic touch, a wand — the entire royal family became in one instant human,” Cashmore said. “It was as if it had dawned on us that they were ordinary people just like us.”

And that changed the royal family.

“Diana jolted them into understanding they weren’t a private institution at all,” Cashmore said. “They were public, and we — the consumers, the fans — felt a sense of entitlement. It’s not just a monarchy. It’s our monarchy.

“The royal family has had to come to the recognition — slowly and rather reluctantly — that they are public property.”

That reluctance — and recognition — was dramatized in “The Queen,” Stephen Frears’ film about the aftermath of Diana’s death, in which the attention-shy monarch played by Helen Mirren is galvanized into a public display of grief by populist Prime Minister Tony Blair.

In the years since Diana’s death, the palace has made increasing concessions to popular hunger, including carefully staged interviews and photo opportunities with the young princes, William and Harry.

Royal officials have media-managed the wedding preparations with skill, releasing a steady drip feed of details, setting up a website, YouTube channel and Twitter account and arranging to stream the wedding ceremony live on the Internet. It is all designed to satisfy huge public curiosity while maintaining some control over the disclosures.

Most people in Britain express nothing but goodwill for William and Kate — and many sympathize with the nervousness Middleton must feel about becoming public property.

“I do think there’s a boundary,” said 23-year-old London trader Leah Clarke. “Every person is human and entitled to their privacy and that’s a right to everyone whether you’re a royal, a celebrity or whatever.”

Perhaps Kate and William will be allowed their fairy-tale ending — or at least a normal existence. Ali hopes so.

“There is a very human part of us that longs for more drama,” she said, “but we would like the fairy tale to work out this time around.”

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Aaron Edwards in London contributed to this report.