Princess Anne missed Prince Harry's christening back in 1984 for this unique reason, as it's reported she was somewhat snubbed by Charles and Diana.
The trouble started in 1977 when Princess Anne and her husband decided to ask the King, who was then known as Prince Charles, to be the godfather of their son, Peter Phillips. The King of course agreed, but didn't return the favour. In 1982 when Prince William was born, Charles and Diana selected distant relatives including, King Constantine II of Greece (his second cousin once removed), Princess Alexandra of Kent (first cousin twice removed), and Lady Susan Hussey to be godparents - but not Princess Anne.
Then when it came to Harry's christening in 1984 his godparents included Prince Andrew, Lady Sarah Chatto, Carolyn Bartholomew, Bryan Organ, Gerald Ward, and Celia, Lady Vestey. Once again, Princess Anne was not selected.
Biographer Robert Lacey explained that it was this snub that upset Anne. "The Prince did not return the compliment when it came to William - or, rather, according to rumour, he had very much wanted to invite his sister, only to be blocked by his wife," writes biographer Robert Lacey in his bestseller Battle of Brothers.
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The author went on to explain it is this snub that led the Princess and her husband at the time, Mark Phillips to miss the christening altogether. "Anne made her feelings obvious on the day. As the three-month-old Prince Henry Charles Albert David, third in line to the British throne, was being baptised as Windsor in the presence of the Queen, the Queen Mother, Philip and the rest of the Royal Family, there were two conspicuous absentees," wrote the author.
The reason given to the public to explain the absence was rather typical for the outdoor-loving Princess Royal. It was reported she had commitments to go hunting instead. "His aunt Anne and her husband Captain Mark Phillips were out in the Gloucestershire countryside, 85 miles to the west, shooting rabbits," wrote the author.
Some defended the Princess and her husband by stating that the hunting party had been planned for a long time, and the couple couldn't let their guests down. "The shooting party took precedence - it was a long-established date," wrote Robert. At the time, Captain Phillips's mother Anne also told the biographer, "The Princess and my son invited a party of 10 guns for shoot three months ago. They decided it would be unfair to let these people down."
Although Princess Anne wasn't selected to be a godparent to Prince Harry or William, Prince Harry and William have selected Princess Anne's children to be the godparents of some of their respective children.
Zara Tindall is godmother to Prince William's eldest son, the future King, Prince George. Prince Harry is also the godfather to his cousin Zara Tindall's second daughter Lena.