Queen Elizabeth will break royal tradition and appoint Britain’s new prime minister at her Balmoral Castle residence in Scotland, not London’s Buckingham Palace.

According to a palace source, the decision was made due to the reigning monarch’s ongoing mobility issues. The 96-year-old usually spends her summers at Balmoral.

A spokesperson for Buckingham Palace confirmed on Wednesday that Elizabeth will meet outgoing Prime Minister Boris Johnson and his successor on Sept. 6. Elizabeth will either be accompanied by Foreign Secretary Liz Truss or former finance minister Rishi Sunak as Britain’s new leader.

As head of state, Britain’s monarch appoints the new prime minister at Buckingham Palace. Every British leader has been appointed there since the reign of Queen Victoria, except on one occasion.

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Queen Elizabeth Boris Johnson

Britain's Prime Minister Boris Johnson resigned in July. (Victoria Jones/Pool/AFP via Getty Images)

In July, the queen’s duties were scaled back due to health concerns.

The annual report of the monarchy revealed that the queen’s role as head of state had been changed from 13 bulleted points to a less specific description, The Sunday Telegraph reported. In addition, those duties the queen "must fulfill" have been removed from the list.

The Sovereign Grant report, which was published following the Platinum Jubilee, places greater emphasis on the support of the royal family in carrying out official royal duties. The queen will be entrusting more to her heir, Prince Charles. The report, signed off by Sir Michael Stevens, Keeper of the Privy Purse, noted that the queen’s role still comprises two key elements: Head of State and Head of Nation.

While Buckingham Palace didn’t comment on the report, a palace source told the outlet that it was not a "drastic" change, but rather "a small update."

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Queen Elizabeth mobility issues

Queen Elizabeth II, who celebrated her Platinum Jubilee this year, has been suffering from mobility issues. (Max Mumby/Indigo/Getty Images)

The move, which was made quietly, is the first change of its kind in more than a decade, People magazine noted.

After the Platinum Jubilee in June, which marked Elizabeth’s 70 years on the throne, she issued a statement emphasizing that she would continue to serve with the support of her family.

"While I may not have attended every event in person, my heart has been with you all; and I remain committed to serving you to the best of my ability, supported by my family," Elizabeth said.

During the Platinum Jubilee, Elizabeth only made a few appearances. Palace officials said she experienced some "discomfort" during those events. But despite her health woes, the queen attended a series of events at Holyroodhouse, her official residence in Edinburgh, Scotland. A smiling Elizabeth, who used a cane, delighted royal watchers.

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Queen Elizabeth

Queen Elizabeth II has been spending her summer in Balmoral. (Max Mumby/Indigo/Getty Images)

Elizabeth pledged to serve Britain and the Commonwealth for her whole life. The queen shows every intention of fulfilling that promise. Still, her problems in getting around have forced her to be more selective in her public engagements. That has opened a door for Charles, who has been ready to step in whenever required.

"Prince Charles is the longest-serving heir we’ve ever had," Robert Hardman, author of "Queen of Our Times: The Life of Elizabeth II," said. "He’s there. He’s on standby to do whatever needs doing if the queen can’t be there. But, you know, she made an oath that she was going to reign for her life. And that’s how she views it."

The Associated Press contributed to this report.