Earl Spencer shared a poignant photo as he marked the anniversary of Princess Diana's death on Tuesday.
The author and historian, 57, posted a social media image of the flag flying at half mast at Diana's family home, Althorp House, as a mark of respect for his late sister.
Charles' followers paid tribute to the late Princess of Wales in the comments, with one writing: "Sending you and your family a lot of love today."
Another said: "May she rest in peace forever our Princess," while a third added: "Eternally young and will be eternally remembered and missed."
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WATCH: Remembering Princess Diana
Diana was tragically killed in a car crash in Paris on 31 August 1997. Her sons, Prince William, and Prince Harry, were aged just 15 and 12 at the time.
Her funeral took place on 6 September 1997 at Westminster Abbey, attended by members of the royal family and a number of high-profile celebrities. Charles delivered a moving eulogy at the service, while thousands lined the streets to pay their respects.
Charles Spencer shared a photo of the flag flying half mast at Althorp House
Princess Diana's final resting-place is in the grounds of Althorp Park in Northampton.
Charles has been custodian of the estate since the death of his father, John Spencer, in 1992, and he regularly shares updates about its beautiful grounds and history.
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The Earl at Princess Diana's statue unveiling in July
The Earl was among a handful of guests to attend a private ceremony on 1 July, where his nephews, William and Harry, unveiled a statue of their late mother in the gardens at Kensington Palace. The date would have marked Diana's 60th birthday.
Charles attended the unveiling alongside his elder sisters, Lady Sarah McCorquodale and Lady Jane Fellowes.
The statue, which depicts Diana with three children, was specially opened to the public on Tuesday to mark the 24th anniversary of her death.
Due to the pandemic, Kensington Palace and its gardens are operating reduced opening days and are usually only accessible to the public from Wednesday to Sunday.
But Historic Royal Palaces (HRP) said special arrangements had been made to allow visitors to view the statue from the Cradle Walk around the Sunken Garden where it stands from 3pm to 5pm on Tuesday.
The Duke and Duchess of Cambridge and their three children – Prince George, Princess Charlotte and Prince Louis – are understood to be commemorating the anniversary privately.
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