Prince William and Prince Harry have some sad news this week as one of their relatives from Princess Diana's side passed away. The Duke of Cambridge and the Duke of Sussex have lost their great-aunt, Lady Anne Wake-Walker, who was the only sibling of their grandfather, John Spencer, the 8th Earl Spencer.

Charles Spencer, the 9th Earl Spencer, and Princess Diana's younger brother, confirmed the death on Twitter. He posted a photo of the Spencer flag flying at half-mast in their family estate, the Althorp House, to honor their departed relative, who was 99 and a half years old.

On Instagram, Charles also paid tribute to his Aunt Anne by posting a photo of her and his father as a toddler from 1925. The earl described Lady Anne as a wonderful lady who served in the Second World War. He also said that Lady Anne was a wonderful mother, sister, aunt, grandmother and great-grandmother.

In 1997 when Princess Diana died, Lady Anne recalled that her royal niece was a "sweet, thoughtful and very kind girl." She also loved Lady Diana's sense of humor.

The Spencer siblings often visited their aunt and her family. Daily Mail has a photo of Lady Diana as a young girl with the Wake-Walkers.

Born to an aristocratic family, Lady Anne was the only daughter of Albert Spencer, the 7th Earl of Spencer, and Cynthia Hamilton. Many of Lady Anne's aunts were the Queen Mother's Ladies-in-Waiting, while Cynthia was the Queen Mothers' Lady-to-the-Bedchamber.

Lady Anne was married to Christopher Baldwin Hughes Wake-Waker in 1944 and they have five children together. One of their daughters was also named Diana, similar to her cousin, the princess. Her husband passed away in 1998 due to an undisclosed disease.

In the book "Diana: The Portrait" by Rosalind Coward, Lady Diana apparently wrote to her aunt following her uncle's diagnosis. The Princess of Wales offered any help she can give her aunt's family, as a patron of the Parkinson's Disease Society.

In 2011, Lady Anne was one of the guests of Prince William and Kate Middleton's wedding. She has a portrait at the National Portrait Gallery in London.

The sad news comes as Prince William and Prince Harry are both attending to their royal duties this week. The Duke of Cambridge visited charities and companies in the Mansfield area while the Duke of Sussex spent a day in Edinburgh for a travel summit.