What was Princess Anne's sharp reaction when she heard that Prince William had been born?
They have had a special royal relationship for a long time.
King Charles and Princess Anne, born just two years apart before their mother became queen, have a special understanding of the monarchy.
As young adults, they went on foreign tours together to represent the Queen.
Today, Princess Anne is seen as Charles' right-hand man: someone who understands what is needed without a word being spoken.
Princess Anne and Prince Charles laugh together in the grounds of Balmoral Castle
Prince Charles and Princess Anne pictured together in 1970. They often worked together in their early years on the front line
King Charles considers his sister, Princess Anne, his right-hand man. They are pictured here at the dedication service at St George's Chapel for their mother, Queen Elizabeth II, in February 2022
Yet there was a period when things were less easy between them, especially in the 1980s when Diana Spencer came into the family.
According to Robert Lacey's Battle of Brothers, Anne's “notorious icy cold seemed to get a few degrees colder when the subject of Diana came up.”
Anne appears not to have been receptive when she was told that Diana had given birth to Prince William in June 1982.
The princess was touring Indian reservations in New Mexico for Save the Children when a reporter asked for her reaction to the good news.
“I didn't know she had one,” the princess snapped.
Another reporter tried it with:
“Do you think everyone is making too much of a fuss about the baby?”
“Yes,” was the short answer.
Why the froideur?
At the time, Lacey says, Anne completed more than two hundred commissions a year, compared to Diana's fifty and just ninety-plus for Charles.
According to Lacey, a Palace insider explained:
'Anne works very hard and sees her sister-in-law taking the credit. She's sick of it.'
Diana with Princess Anne at a polo match near London the weekend before Diana's wedding
Apparently icy times on the balcony for Trooping the Color in 1983
Princess Diana and Princess Anne at the Cenotaph commemorating Sunday 1983
Princess Anne attends a private reception given by the Governor of New Mexico in 1982 at the Palace of the Governors. When asked about the birth of Prince William, Charles and Diana's first child, she seemed irritated
Prince William arrived on June 6, 1982, to the delight of the nation and the world's press camped outside the Lindo Wing. Princess Anne didn't seem too thrilled at the time
Press photographers wait outside the Lindo Wing of St Mary's Hospital after Prince William's birth in 1982
Prince Charles and Princess Diana leave St Mary's with their son
The Prince and Princess of Wales left The Lindo Wing in the back of a car with Prince Charles and the new baby
Diana, Princes of Wales, surrounded by family and friends, holds infant son Prince William as she sits with Queen Elizabeth II and Queen Elizabeth, the Queen Mother, in August 1982. Princess Anne sits on the armrest of the sofa, directly behind her mother
A group portrait on the occasion of the baptism of Peter Phillips in December 1977. Prince Charles, who was asked to be godfather, is second from the left
A photo taken at Prince Harry's christening at Windsor Castle on December 21, 1984. The royal family members appear amused by the antics of young Prince William. Princess Anne was not among the guests. She was in Gloucestershire shooting rabbits
The depth of the bad feeling was revealed shortly afterwards when, although Anne had asked Charles to be a godparent to her first child, Peter Phillips, the compliment was not returned.
Anne was not invited to become William's godmother and was not on the list when it was Prince Harry's turn to be baptized in 1984.
The princess made her feelings clear, Lacey says. While Harry was carried to the fountain at St George's Chapel in Windsor, Anne was shooting rabbits with her husband in the Gloucestershire countryside.