Kate Middleton to return to the spotlight at dinner commending Queen Elizabeth's landmark reign

Duchess of Cambridge

Kate Middleton and her daughter Charlotte in the official christening portrait

Catherine, Duchess of Cambridge and Prince William, Duke of Cambridge attend day nine of the Wimbledon Lawn Tennis Championships at the All England Lawn Tennis and Croquet Club on July 8, 2015 in London, England. (Photo by Ian Walton/Getty Images)

Catherine, Duchess of Cambridge and Prince William, Duke of Cambridge attend day nine of the Wimbledon Lawn Tennis Championships at the All England Lawn Tennis and Croquet Club on July 8, 2015 in London, England. (Photo by Ian Walton/Getty Images)

Catherine Duchess of Cambridge attends the Gigaset Charity Polo Match with Prince George of Cambridge at Beaufort Polo Club on June 14, 2015 in Tetbury, England. (Photo by Chris Jackson/Getty Images)

The Duke and Duchess of Cambridge and their children, Prince George and Princess Charlotte who was christened at Sandringham on Sunday. Credit: Mario Testino / Art Partner

Catherine, Duchess of Cambridge, Prince William, Duke of Cambridge, Princess Charlotte of Cambridge and Prince George of Cambridge arrive at the Church of St Mary Magdalene on the Sandringham Estate for the Christening of Princess Charlotte of Cambridge on July 5, 2015 in King's Lynn, England. (Photo by Chris Jackson - WPA Pool/Getty Images)

thumbnail: Duchess of Cambridge
thumbnail: Kate Middleton and her daughter Charlotte in the official christening portrait
thumbnail: Catherine, Duchess of Cambridge and Prince William, Duke of Cambridge attend day nine of the Wimbledon Lawn Tennis Championships at the All England Lawn Tennis and Croquet Club on July 8, 2015 in London, England.  (Photo by Ian Walton/Getty Images)
thumbnail: Catherine, Duchess of Cambridge and Prince William, Duke of Cambridge attend day nine of the Wimbledon Lawn Tennis Championships at the All England Lawn Tennis and Croquet Club on July 8, 2015 in London, England.  (Photo by Ian Walton/Getty Images)
thumbnail: Catherine Duchess of Cambridge attends the Gigaset Charity Polo Match with Prince George of Cambridge at Beaufort Polo Club on June 14, 2015 in Tetbury, England.  (Photo by Chris Jackson/Getty Images)
thumbnail: The Duke and Duchess of Cambridge and their children, Prince George and Princess Charlotte who was christened at Sandringham on Sunday. Credit: Mario Testino / Art Partner
thumbnail: Catherine, Duchess of Cambridge, Prince William, Duke of Cambridge, Princess Charlotte of Cambridge and Prince George of Cambridge arrive at the Church of St Mary Magdalene on the Sandringham Estate for the Christening of Princess Charlotte of Cambridge on July 5, 2015 in King's Lynn, England.  (Photo by Chris Jackson - WPA Pool/Getty Images)
Caitlin McBride

Kate Middleton is set to return to the spotlight next week to celebrate Queen Elizabeth's milestone as the longest reigning British monarch.

The Duchess of Cambridge has been absent from public engagements of late, focusing on her growing family at her mansion in Norfolk.

Kate and her husband of four years, Prince William, welcomed their second child Princess Charlotte into the world in May and celebrated Prince George's second birthday last month.

The royal couple have been formally invited to celebrate the Queeen's landmark occasion at her home in Balmoral, Scotland on September 9.

Prince George of Cambridge is held by Prince William, Duke of Cambridge and Catherine, Duchess of Cambridge, Prince Charles, Prince of Wales and Queen Elizabeth II look out on the balcony of Buckingham Palace during the Trooping the Colout

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"The Duke and Duchess of Cambridge will be with the Queen at Balmoral on September 9," a source told the Daily Mail.

"They will attend a family dinner that Her Majesty will give that evening."

Catherine, Duchess of Cambridge and Prince William, Duke of Cambridge attend day nine of the Wimbledon Lawn Tennis Championships at the All England Lawn Tennis and Croquet Club on July 8, 2015 in London, England. (Photo by Ian Walton/Getty Images)

Similar to when she welcomed Prince George in 2013, Kate has preferred to take a step back from her royal duties on maternity leave for the month of August.

It comes as the couple have pleaded for personal privacy, in particular regarding paparazzi images of their children.

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Catherine Duchess of Cambridge attends the Gigaset Charity Polo Match with Prince George of Cambridge at Beaufort Polo Club on June 14, 2015 in Tetbury, England. (Photo by Chris Jackson/Getty Images)

In an open letter penned by the Duke and Duchess, they slam photographers who are employing these "dangerous" and "distressing" tactics.

According to The Telegraph, the letter reveals that paparazzi have been found hiding on private fields and woodland at the family's Norfolk home, obscuring themselves in sand dunes to take photographs of Prince George playing with his grandmother and monitoring the movements of the toddler, his nanny and other household staff around London parks.

Diana, Princess of Wales, wearing an Emanuel wedding dress, leaves St. Paul's Cathedral with Prince Charles, Prince of Wales following their wedding on 29 July, 1981 in London, England. (Photo by Anwar Hussein/Getty Images)

Lady Diana Spencer visits Tetbury in Gloucestershire May 22, 1981, two months before her marriage to Prince Charles, Prince of Wales. Prince Charles's Highgrove residence is near Tetbury. (Photo by Anwar Hussein/WireImage)

Princess Diana(L) and her son Harry(R) watch veterans as they march past a dais on the Mall as part of the commemorations of VJ Day 19 August.

NOV 1996 - PRINCESS DIANA, THE PRINCESS OF WALES ARRIVING AT THE VICTOR CHANG CARDIAC RESEARCH INSTITUTE DINNER DANCE IN SYDNEY , AUSTRALIA. (Photo by Patrick Riviere/Getty Images)

The late Princess Diana

GALLERY:

It says that on one "disturbing but not at all uncommon" occasion, a photographer hid himself in a rented car near a children's play area, hanging sheets in the windows and stockpiling enough food and drink to get him through a full day of surveillance.

Catherine, Duchess of Cambridge, Prince William, Duke of Cambridge, Princess Charlotte of Cambridge and Prince George of Cambridge arrive at the Church of St Mary Magdalene on the Sandringham Estate for the Christening of Princess Charlotte of Cambridge on July 5, 2015 in King's Lynn, England. (Photo by Chris Jackson - WPA Pool/Getty Images)

Police found the man lying down in the boot of the vehicle attempting to shoot photos with a long lens through a small gap in his "hide".

Royal insiders claim that William is increasingly nervous and worried that "history might repeat itself" as his family are becoming susceptible to the media intrusion experienced by his late mother Diana, Princess of Wales.

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The Duke firmly believes that paparazzi photographers in Paris were ultimately responsible for his mother’s death in 1997, when her car crashed at speed in an underpass following a pursuit by photographers on mopeds.

The letter, sent to 24 worldwide media industry watchdog bodies, says it is clear that Prince George had become the "number one target" in the Royal Family for unscrupulous freelance photographers who sell their images abroad.