Why Prince George's Country Years Will Be Short-Lived

 
From playing in the fields near his family home, Anmer Hall, to rambling through the woods of his mom's childhood village of Bucklebury, Prince George is growing up to enjoy every aspect that the beautiful British countryside has to offer.

Yet the future king – who turned three on July 22 – will likely be pulled away from the quiet rural life that parents Princess Kate and Prince William wish for him and sister Princess Charlotte, 15 months.

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With George's "Gan-Gan"Queen Elizabeth having turned 90 in April, it is likely that William and Kate will start to take on an ever-increasing number of royal duties.

The royal parents understand that as long as there are "three generations of royals doing public duties," as a friend tells PEOPLE in this week's cover story, there is less pressure on them.

"The difference will come when they have to spend more time in London" as the Queen and her husband Prince Philip, 95, cut back on their public duties, the friend adds.

"The moment that [Prince] Charles becomes king, it is over," says royal historian Robert Lacey. "William will definitely have to come down to London and Kate too."

For much more on Prince George's amazing life, pick up this week's issue of PEOPLE, on newsstands Friday