Prince William and Kate Middleton Are Ready to Lead a Modern Monarchy: 'You Couldn't Have Got a Better Pair'

With their 40th birthdays on the horizon, Kate Middleton and Prince William are all set to step up, remaking the Windsor family in their own image as they prepare to lead it later this century.

The fall cover story of PEOPLE Royals' special quarterly edition (out September 10) outlines how the Duke and Duchess of Cambridge have, together, come up with a set of successful rules that have helped them navigate royal and family life for a decade — and that will set them up for the future.

Much of their magic stems from their different backgrounds. Kate, from a hard-working family, provides the perfect balance for William the future king, and they support one another. "They are bringing to the party different means of achieving the whole," their former private secretary Jamie Lowther-Pinkerton tells PEOPLE Royals.

"He has the experience of knowing where the institution sits and seeing it evolve," continues Lowther-Pinkerton. "The Duchess brings this pragmatic awareness of what it's like to be from a decent, down-to-earth family."

Focusing on initiatives from mental health and parenting to climate change, they "are playing a really important role in finding a point of connection for a different range of subjects that the family hasn't always connected with," says a former staffer.

For much more on the couple and their 10-year marriage and what the future holds, pick up a copy of PEOPLE Royals, on newsstands September 10.

Their bond comes from a base forged in a long courtship and a strong marriage. And thanks to the examples of Kate's parents, Carole and Michael Middleton, and Queen Elizabeth and Prince Philip's 73-year marriage in the public eye, William and Kate are ready for what is ahead.

As the couple bridges their lives now with the future they envision at the helm of the monarchy, a family friend says they "can mix the traditional duty with being thoroughly modern parents."

Theirs is a shared burden, and William said in 2016, "I take my duties and responsibilities to my family very seriously." Since then, Prince Louis, now 3, has joined siblings Prince George, 8, and Princess Charlotte, 6. The trio are being raised between Kensington Palace in London and in the country at Anmer Hall in Norfolk, where they pursue active, fun-filled lives.

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Now that Prince Harry and Meghan Markle are no longer working as frontline royals, more attention is falling on the Cambridges — not necessarily in terms of the number of engagements or duties, but "in being the modern face of the institution," adds a palace insider.

And when their time comes, William and Kate will be fully prepared.

"Thank God they've got each other and the training that they've had," says Lowther-Pinkerton. "They have a solid bond through these last 10 years. If you had scoured the realm you couldn't have got a better pair, frankly."