Prince William and Prince Harry Unite in Special Message for Charity Close to Their Hearts

Queen Elizabeth II 's grandchildren (L-R) Britain's Prince Harry, Duke of Sussex (L) and Britain's Prince William, Prince of Wales (R) arrive to hold a vigil around the coffin of Queen Elizabeth II, in Westminster Hall, at the Palace of Westminster in London on September 17, 2022, ahead of her funeral on Monday. - Queen Elizabeth II will lie in state in Westminster Hall inside the Palace of Westminster, until 0530 GMT on September 19, a few hours before her funeral, with huge queues expected to file past her coffin to pay their respects. (Photo by Aaron Chown / POOL / AFP) (Photo by AARON CHOWN/POOL/AFP via Getty Images)
Queen Elizabeth II 's grandchildren (L-R) Britain's Prince Harry, Duke of Sussex (L) and Britain's Prince William, Prince of Wales (R) arrive to hold a vigil around the coffin of Queen Elizabeth II, in Westminster Hall, at the Palace of Westminster in London on September 17, 2022, ahead of her funeral on Monday. - Queen Elizabeth II will lie in state in Westminster Hall inside the Palace of Westminster, until 0530 GMT on September 19, a few hours before her funeral, with huge queues expected to file past her coffin to pay their respects. (Photo by Aaron Chown / POOL / AFP) (Photo by AARON CHOWN/POOL/AFP via Getty Images)

AARON CHOWN/POOL/AFP via Getty Prince William and Prince Harry

Prince William and Prince Harry united in a message for a special family close to them this week.

The Prince of Wales, 40, and the Duke of Sussex, 38, jointly signed a letter praising the work of a charity they both support, and honor a family "we all love and adore."

Their message came at the annual carol service raising money for the Henry van Straubenzee Memorial Fund, a non-profit that was set up by the parents, Alex and Claire, and brothers of their late friend, Henry van Straubenzee.

The royal brothers are patrons of the charity and have been attendees — and speakers — along with their wives, Kate Middleton and Meghan Markle, at the festive event in the past.

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The charity supports schools and helps construct, restore and improve buildings, enabling children to have better and properly-equipped classrooms and facilities like restrooms. When he died in a car crash in 2002, Henry had been due to travel to Uganda to work in a school during his gap year.

Mandatory Credit: Photo by Kirsty O'Connor/AP/Shutterstock (13381259a) From left, Kate, the Princess of Wales, Prince William, Prince of Wales, Prince Harry and Meghan, Duchess of Sussex walk to meet members of the public at Windsor Castle, following the death of Queen Elizabeth II on Thursday, in Windsor, England Royals, Windsor, United Kingdom - 10 Sep 2022
Mandatory Credit: Photo by Kirsty O'Connor/AP/Shutterstock (13381259a) From left, Kate, the Princess of Wales, Prince William, Prince of Wales, Prince Harry and Meghan, Duchess of Sussex walk to meet members of the public at Windsor Castle, following the death of Queen Elizabeth II on Thursday, in Windsor, England Royals, Windsor, United Kingdom - 10 Sep 2022

Kirsty O'Connor/AP/Shutterstock Prince William, Kate Middleton, Prince Harry and Meghan Markle at Windsor Castle

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Henry's brothers Thomas and Charlie remain close to the princes and are godparents to William's daughter Princess Charlotte and Harry's son Archie, respectively.

William and Harry's jointly-signed letter was carried in the order of service at Thursday's carol service, which was attended by close friends, including Princess Kate's sister and brother, Pippa and James, and their spouses, at St. Luke's Church, in Sydney Street, Chelsea.

Prince Harry and Prince William, Duke of Cambridge shake hands after competing against each other in the Sentebale Polo Cup polo match at Coworth Park Polo Club on June 12, 2011 in Ascot, United Kingdom.
Prince Harry and Prince William, Duke of Cambridge shake hands after competing against each other in the Sentebale Polo Cup polo match at Coworth Park Polo Club on June 12, 2011 in Ascot, United Kingdom.

Indigo/Getty Prince Harry and Prince William in happier times in 2011

Together, the princes wrote, "We believe everyone here tonight will agree that what Claire and Alex have achieved since 2009 ... is nothing short of extraordinary. As you gather under this roof tonight, the charity is supporting 51 nursery, primary and secondary schools in rural Uganda, where 1,700 projects have been completed and over 35,000 children, each year, are benefitting by receiving education they wouldn't have otherwise had."

"For those of us who knew Henners, we will always miss his mischievous charm and hilarious sense of humor," they continued.

And though the brothers noted that the charity will be gradually wound down, the letter said, however, that "Henry's legacy will live on through the incredible achievements of what his mum and dad have accomplished over the years."

Wishing everyone an "enjoyable evening and very Happy Christmas," the letter concluded: "As long as funds permit, they will continue to monitor their schools, enduring that the children of south east Uganda receive that vital education, providing the opportunity to escape poverty as they grow up, and hopefully that of their own children in the future. Thank you for your continued support in making this possible, and for the everlasting support of the van family who we all love and adore."

Britain's Prince William, Prince of Wales, and Catherine, Princess of Wales, arrive for the 2022 Earthshot Prize ceremony at the John F. Kennedy Presidential Library and Museum in Boston, Massachusetts, December 2, 2022. (Photo by ANGELA WEISS / AFP) (Photo by ANGELA WEISS/AFP via Getty Images)
Britain's Prince William, Prince of Wales, and Catherine, Princess of Wales, arrive for the 2022 Earthshot Prize ceremony at the John F. Kennedy Presidential Library and Museum in Boston, Massachusetts, December 2, 2022. (Photo by ANGELA WEISS / AFP) (Photo by ANGELA WEISS/AFP via Getty Images)

ANGELA WEISS/AFP Kate Middleton and Prince William

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The princes couldn't be at the carol service in-person for different reasons.

William landed back in Britain on Saturday morning alongside Kate, 40, after their three-day trip to Boston, which ended with the triumphant Earthshot Prize ceremony at the MGM Grand at Fenway.

Harry, meanwhile, was in California, where he lives with Meghan, 41, and their children, son Archie, 3, and daughter Lilibet Diana, 1.