Prince William and Prince Harry recently joined their mother’s side of the family at a memorial service for their late uncle, Lord Robert Fellowes

(Left) Prince William at the RAF College in Cranwell on Sept. 12, 2024; (Right) Lady Sarah McCorquodale in London on Sept. 20, 2013. . Photo: Karwai Tang/WireImage; Max Mumby/Indigo/Getty Images

Princess Diana’s sister Lady Sarah McCorquodale made a rare appearance at Prince William’s latest engagement.

On Sept. 12, Lady Sarah, 69, supported her nephew at the Sovereign’s Parade at the Royal Air Force (RAF) College in Cranwell, Lincolnshire, England. The Prince of Wales, 42, appeared at the graduation on behalf of his father King Charles, and Rebecca English of the Daily Mail reported that Sarah was there.

“I’m told she heard he was in the area and wanted to support him,” English wrote on X. Her post included a video seeming to show Lady Sarah in the background while Prince William chatted at a reception after the parade, where he joined graduating officers and their loved ones to learn more about their experiences at RAF Cranwell and hopes for their future careers.

Prince William referenced his own training at RAF Cranwell in a speech — and promised to keep his remarks brief.

Prince William at RAF College Cranwell on Sept. 12, 2024.OLI SCARFF/POOL/AFP via Getty

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“Whilst I didn’t graduate on this exact Parade Ground, I did graduate from flying training here, so I know something about the celebrations that will come later — so I promise I’ll only take a few minutes of your time!” the Prince of Wales jokingly told the graduates.

The royal also acknowledged the role of those who supported the latest class of RAF cadets elsewhere in his message. “To the families and friends gathered here — thank you for your encouragement and understanding to get these brilliant men and women this far, and for the empathy, compromise and dedication that will be required to give these officers every chance of success in their careers,” he said.

William earned his wings at the airbase in 2008 in a ceremony that Kate Middleton, King Charles, the future Queen Camilla and Lady Sarah all attended.

Prince William and Kate Middleton at his graduation ceremony at RAF Cranwell on April 11, 2008. Pool/Anwar Hussein Collection/WireImage

Sarah is the late Princess Diana’s eldest sister, and Hello! noted that she doesn’t live far from RAF Cranwell.

While her life is outside of the spotlight, much like Diana’s other sister Lady Jane Fellowes and brother Charles Spencer, she (and her siblings) have stepped out to support Prince William and Prince Harry plenty of times before.

Prince Harry, Lady Sarah McCorquodale, Prince William and Lady Jane Fellowes at the unveiling of Princess Diana’s memorial state in the Sunken Garden at Kensington Palace on July 1, 2021.DOMINIC LIPINSKI/POOL/AFP/Getty

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Lady Sarah and Lady Jane, 67, were there when Prince William and Prince Harry, 39, unveiled Princess Diana’s memorial statue at Kensington Palace on what would have been her 60th birthday in July 2021, and they all came together again recently at the memorial service for Jane’s late husband, Lord Robert Fellowes, on Aug. 29. Robert, who spent much of his career in the royal household and served as Queen Elizabeth’s private secretary from 1990 to 1999, died on July 29 at age 82 of undisclosed causes, and was honored at the private service in Norfolk one month later.

Prince Harry’s unexpected transatlantic travel to pay his respects was deeply emotional, leaving him “pleased” and guests “astounded,” a source told PEOPLE.

The trip carried significance, coming just two days ahead of the anniversary of Princess Diana’s death following a car accident in Paris on Aug. 31, 1997. However, Harry’s surprise arrival in the U.K. — despite earlier reports that he wouldn’t attend — didn’t lead to a public reconciliation with his brother, William, amid their ongoing rift.

At the service at St. Mary’s Church in Snettisham, the estranged brothers sat apart, each with different groups of their maternal cousins.

Prince William and Prince Harry on the Long Walk at Windsor Castle on Sept. 10, 2022.Chris Jackson – WPA Pool/Getty Images

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“Most people were astounded that Harry came,” one of the reported 300 attendees told PEOPLE. “He was on remarkably good form — and you could tell he was very pleased to see everybody. And he was very pleased that he had come over.”

PEOPLE further learned that the Duke of Sussex stayed with his uncle Charles, the 9th Earl Spencer, at Althorp House following his surprise appearance at the memorial service. Althorp is the Spencer family’s ancestral estate in Northamptonshire and is where Princess Diana is buried.

In May, Lady Jane, Earl Spencer and several of the Spencer cousins supported Prince Harry at the 10-year anniversary service for the Invictus Games at St. Paul’s Cathedral in London, which no senior members of the royal family attended. Harry’s appearance at his late uncle’s memorial and stay at Althorp reaffirms his strong bonds with his mother’s side of the family.