It should be a time of celebration for the Beckham brood – having just marked Victoria’s 50th birthday with a star-studded party, plus the couple’s 25th wedding anniversary coming up this summer.

But there’s one big elephant in the room that’s overshadowing the festivities: bestselling author Tom Bower’s tell-all book, which is due out in June, just two weeks before their milestone anniversary.

The book, titled The House Of Beckham: Money, Sex And Power, promises to deliver a “revealing tour of the lives of one of the world’s most famous and influential power couples”,

including never-before-seen sourcing and interviews with insiders. And despite fans feeling excited to glimpse behind the perfect façade of Posh, 50, and Becks,

48, we’re told Victoria is terrified about what secrets could be unearthed in the book’s bombshell 320 pages.

Now, a source tells heat, “When the blurb for the book includes the line, ‘Are their lives really as perfect as the Beckhams would like the world to believe?’ Then, it’s already pretty ominous.

This is Vic’s worst nightmare – everything she has done in her life has been about presenting a picture of perfection to create a powerful personal brand. For the critics of her singing abilities, for those who thought David could do better, that she wasn’t good looking enough for him or talented enough to be a fashion designer – whenever Vic felt under threat, her reaction has been to present this image of invincible perfection.”

The insider continues, “A book about their ‘untold story’ is a daunting promise, and Vic and David have both been extremely on edge about what may come out and how it could ruin everything they’ve built. The Beckhams’ rags-to-riches story didn’t come without struggles. They built up a brand and a business based on leveraging their appeal as a couple into an ability to make money – and they’ve had their fair share of dramas behind closed doors.

“There’s been business relationships that didn’t work out, rivalries and power struggles, as well as people looking to use them. Lots of things have ended in acrimony, and to have someone come along, seemingly with the intent of peeling back that perfect veneer, is terrifying to Victoria. There’s the life they’ve served up as Brand Beckham, and then there’s the dramas of life as a showbiz couple who got together in their early twenties.”

The couple’s appeal reached new heights last year, following the release of David’s hit Netflix documentary Beckham. The series gave fans an insight into the many storms the couple have weathered together in their over 20-year romance: from David’s rise to footballing fame, the heady days of Posh and Becks, and David’s battle with depression following his 1998 World Cup exit.

Our source says, “The early years of the marriage were pretty crazy. They were intense, and there was a lot of drama. After all, they were both young and in the spotlight, with their heads spinning from global success and money being thrown at them. There’s been lots of cheating rumours, as well as celeb feuds and fallings out with lots of people, from Tom Cruise to Cheryl Cole and a few WAGs. Then there’s the personal stuff, such as Vic’s eating habits, the kids’ lives, and all the wedding drama with Nicola and Brooklyn.”

And while there’s plenty of potentially salacious fodder that could find its way into Tom’s book, the biggest potential bump in the Beckhams’ road, which could cover more than a few pages, is David’s rumoured affair with Rebecca Loos. Back in 2003, it was alleged that David had been involved in an affair with his then personal assistant Rebecca, which reportedly took place while the footballer was playing for Real Madrid in Spain. David and Victoria briefly addressed the rumours in Beckham – not confirming them, but instead reflecting on how the tidal wave of media attention affected their marriage.

Admitting that period of time was the “unhappiest” she had ever been, Posh revealed, “Up until Madrid, sometimes it felt like us against everybody else. When we were in Spain, it didn’t really feel like we had each other either.”

With the alleged affair now likely to be dragged up once more, we’re told, “Vic feels like she’s lived her life with the title of ‘the most-cheated-on woman in Britain’, because of the Rebecca Loos story – it’s like having a cartoon rain cloud hovering over her head. The one thing she does not need is revival of the narrative of a woman destroyed and broken by the man she adored – her dream of a forever love and perfect life crushed and her trust gone.”

But there’s more than just VB’s image at stake. With the book set to reveal a number of bombshells about the couple, we’re told that Victoria is determined to shelter the couple’s children Brooklyn, 25, Romeo, 21, Cruz, 19, and Harper, 12, from any potential fallout.

“Tom Bower seems determined to pry open old wounds, putting not just Victoria and David through the wringer, but their families and their kids, too,” says the source. “Vic is furious. She and David have spent the last few weeks trying to come up with a containment strategy and figure out who may have spoken to Tom.”

We’re told that Victoria is also turning to David for damage control – urging him to come clean about any final secrets before the book’s release. “They took a day away from everything recently to sit down and go over stuff – they’re preparing for any eventuality,” the source reveals. “Vic did beg David to let her know if there’s any more skeletons in the closet, but he promised her that they’re on the same page.”

As they prepare for what’s to come, Posh and Becks are putting on a united front – and looked closer than ever at Victoria’s big birthday party last week. As the couple celebrated with A-list friends and family, including all four of their children, they didn’t appear to have a care in the world – with David even giving his tipsy wife a piggyback to their car after leaving at 2.30am.

But behind the unfazed exterior, we’re told that VB can’t help but feel sad. Despite their recent successes, it’s only a matter of weeks until the book’s publication throws the couple’s marriage and legacy back into the spotlight.

The source explains, “It really stung Vic when so many people used to question what David was doing with her. She’s spent her life trying to prove that she is good enough for him, that she really is a global pop star, a fashion designer, a perfect mother, ageless and with a flawless figure. That’s one of the biggest secrets she doesn’t want to come out – just how much she cares. She’s spent her life trying to control their public image, and now she feels that slipping away.”