In May 2015, the staff of Vanity Fair was on top-secret lockdown, shooting a cover that was soon to become their biggest ever: Olympian gold medallist Bruce Jenner’s transformation to a woman named Caitlyn Jenner.

Star photographer Annie Leibovitz was on board to photograph the 6-foot-2 Jenner, towering over everyone at the shoot in her high heels.

Cellphones were confiscated from everyone on the set. Vanity Fair’s security team, headed by Keith Duvall, a former NYPD cop, were stationed around Jenner’s Malibu, Calif., house with binoculars and walkie-talkies. They were checking for hidden paparazzi, incoming drones, any breach in security.

Suddenly, security announced: “There’s a Bentley coming up the hill.”

It was Kim Kardashian, Jenner’s former stepdaughter, and her arrival was a possible security breach as the paparazzi generally trail her where ever she goes.

The reality star, it seemed, wanted in on what promised to be an iconic cover of Vanity Fair.

She went through the security checkpoint, turned over her cellphone and walked into the house in full makeup, camera-ready.

There was just one problem with her plan. Vanity Fair had a ban on any Kardashian appearing in the magazine.

“It was a cultural cold war. No one was happy to see her on this day,” writes Dana Brown in his book “Dilettante: True Tales of Excess, Triumph and Disaster” (Ballantine).

Brown, then deputy editor of Vanity Fair, and Buzz Bissinger, who was on board to write the story, escorted Kardashian to the kitchen.

“With no reality TV cameras around … she was just Kim, a normal human being whose equally famous stepfather was in the next room in heels and a wig, not to mention with new breasts,” writes Brown.

“Kim said she was proud of her stepfather, excited for the world to meet Caitlyn. But she was less interested in us than she was in getting into one of Annie’s photographs.”

Kardashian listened to the voices and popping strobes in the next room, but was also distracted by the tray of crudités and dip sitting in front of her.

“She wanted to grab a carrot or celery stalk but held back … She didn’t want to mess up her perfectly lined lips, let alone have a piece of celery stuck in her teeth,” writes Brown.

After half an hour, they had run out of things to say to each other, and Kim accepted the reality that she wasn’t going to be photographed with Jenner. When she finally decided to leave, she grabbed a carrot and stalk of celery on her way out.

The Caitlyn story brought 9 million readers to the Vanity Fair website in the first 24 hours — and proved that the internet was now the newsstand.

Brown had a front-row seat to all sorts of A-list shenanigans during his two-and-a-half decades at Vanity Fair, which he began in 1994 at age 20. Prior to that, he was working as a barback at Restaurant 44, a trendy restaurant in the Royalton Hotel on West 44th Street which was a stone’s throw from the offices of Condé Nast — publisher of Vanity Fair, Vogue, The New Yorker and other magazines — then located at 4 Times Square.

The restaurant was Anna Wintour’s favorite spot, and the Vogue editor-in-chief was always treated like royalty there. The staff had an unofficial, unspoken Anna Wintour user manual, detailing how she must be treated.

Upon her arrival, Wintour was never asked if she would care to check her coat. Instead, she would swiftly walk to her usual table and dramatically drop her coat, which was caught by the manager or another employee. At table No. 1, she was surrounded by such A-listers as her boss, Si Newhouse, chairman of Conde Nast, and the company’s other big-name editors — Tina Brown of The New Yorker, who had moved over from editing Vanity Fair; and Graydon Carter, who succeeded Brown at Vanity Fair in 1992.

The second Wintour sat down, a cappuccino was to be placed in front of her. That sometimes required the restaurant’s barista to prepare as many as 10 cups to achieve the perfect temperature if she arrived early or late for her reservation.

“If you were to create a fashion editor in a lab, you would have created Anna Wintour, down to her auburn bob, dark glasses and disinterested demeanor,” writes Brown. “This was the power lunch as scripted by Shakespeare, ‘Game of Thrones’ as written by Truman Capote.”

When Brown got the call from Carter in 1994 to join Vanity Fair as his assistant, Carter’s only advice to Brown was “Don’t f–k it up.”

They soon bonded and would hang out in Carter’s office, where the editor-in-chief pontificated about the magazine business and life while they smoked cigarettes. On one occasion, Carter once invited Brown in, grinning and holding up what looked like a pen. But when he clicked the “pen,” a red dot appeared on the ceiling. It was a laser pointer, and Carter suggested they “mess with some people.”

Moving over to the window, Carter beamed the red dot on a bank employee in a building at 45th and Madison, ducking and giggling when the man looked up. He and Brown took turns nailing more bank employees as well as people on the street, hiding when people looked around for the source.

A few days later police detectives paid them a visit.

“We played dumb to the cops. ‘What’s a laser pointer?’ — collapsing into hysterics after they’d gone, like true idiots,” writes Brown.

During Fashion Week in 1996, Vanity Fair threw a party for the opening of Italian fashion designer Valentino’s new Madison Avenue flagship store. Brown was assigned to work the door.

On the day of the party, Brown got a call from publicist-turned-manager Jason Weinberg, whose clients included Donald Trump’s second wife, Marla Maples, trying to get a start as an actress. Maples “really wanted to come to dinner that night,” pleaded Weinberg. Could they squeeze in her and Trump?

The answer was no, dating back to a long-raging battle between Trump and Carter, when the editor dubbed Trump “the Short-Fingered Vulgarian” in a 1984 story for Spy magazine: “The hands are small and neatly groomed.”

The name threw Trump into a rage, and over the years he would send Carter pictures of himself from other magazines or newspapers, with his hands circled and the line “See, not so small!” written on the page.

By 1996, Trump had calmed down a bit, but there was still no room at the dinner. The couple could, however, attend the after-dinner party, Brown offered.

Instead, Trump and Maples simply showed up at the dinner in a stretch limo.

He approached Brown and was told, “You were not invited.” There were simply no more seats.

“Do you know who I am?” Trump asked.

“The Donald went f–ing off on me … his little mouth spitting invective, his hands spinning around like tiny little propellers,” recounts Brown.

The couple climbed back into the limo and sped off.

Weinberg was put in another difficult situation when he accompanied Courtney Love to the 2006 Vanity Fair Oscar party.

Love was on the guest list but Weinberg wasn’t. When Love asked Sara Marks, then Vanity Fair’s director of Special Projects, to let him in the answer was no.

Irate, Love entered the party, went over to the press line and yelled “Sara Marks is a c–t!”

Carter retired in December 2017, and suggested Brown seek his job. Instead, he was laid off, along with several other longtime editors at the magazine, in 2018. (Radhika Jones was hired for the role.) But Brown has few regrets.

“I did live in a fantasy for 25 years,” he writes. “A gilded bubble — and it was great.”