Inside Queen Elizabeth and Prince Phillip's Secret To Their 70 tahun Marriage Despite Early Troubles 

Queen Elizabeth fell head-over-heels for Prince Philip when she was just a teen, and now they are celebrating 70 years together!

for an inside look into their untold love story – only in PEOPLE!

Guests at a small reception held near Windsor Castle earlier this year were treated to a first-hand look at a remarkable partnership: the 70-years-strong marriage of Queen Elizabeth and Prince Philip.

Effortlessly greeting the assembled group, straight-talking Philip, 96, was “as switched on as ever,” one attendee tells PEOPLE in this week’s cover story. And as his more reserved wife, 91, chatted to others, it was clear how much she relies on her other half.

Elizabeth and Philip on their honeymoon on Nov. 24, 1947 at Broadlands, an estate in the English countryside.

“Part of the reason she keeps going so steadily is that she has him there beside her,” says the attendee. “They’re a great team, and that’s still the case.”

The couple’s 70th anniversary on Nov. 20 — which they plan to celebrate privately with family at Windsor Castle — is yet another major milestone for the Queen, who in 2015 surpassed Queen Victoria as the longest-reigning British monarch in history. By her side since their wedding on Nov. 20, 1947 has been Philip, whose confidence and unscripted humor have long balanced Elizabeth’s shy nature.

“He’s someone who can be frank and someone she can have a laugh with,” says royal biographer Robert Hardman, author of 

. Elizabeth was just 13 when she first fell for the charming Philip, then an 18-year-old dashing Royal Navy cadet with “piercing blue eyes,” as Elizabeth’s governess later described him.

The royal couple revisited Broadlands for their 60th wedding anniversary in 2007.

For more on the Queen and Philip’s life together and their platinum wedding anniversary pick up the latest issue of PEOPLE on newsstands on Friday.

As in any marriage, there have been tensions and conflicts through the years. Rumors of a wandering eye long dogged Philip, with the couple often spending time apart. “There was his polo and carriage driving for decades, when he would quite regularly be away for the weekend,” says historian Robert Lacey, a consultant for the Netflix hit

(The series focuses on these tensions in season two, which starts streaming Dec. 8.)

RELATED VIDEO: Queen Elizabeth Is a High-Stakes Horse Breeder Who Has Raked in How Much at the Races?!

Still, notes Lacey, “He was always staying in the home of mutual friends. The Queen’s friends are solid, moral people, and I don’t think there was any suggestion that friends were turning a blind eye to things that the Queen wouldn’t approve.”

And while Philip at times chafed at his second-fiddle public role of the Queen’s consort, at home he was always king of the castle.

“Within the marriage, [Philip] was in charge of virtually everything,” says Lacey.

Before their upcoming anniversary celebration, the couple will appear together on Nov. 12 at the Cenotaph memorial in central London to honor Britain’s fallen soldiers. But breaking longstanding tradition, time the Queen will stand alongside her husband on the balcony to watch as their eldest son Prince Charles solemnly lays a wreath on her behalf.

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