Prince William posted a rare throwback picture of himself with Prince Harry and Princess Diana to honor the 999 Day in the United Kingdom, also known as Emergency Services Day.
Recently, The Duke of Cambridge's office at Kensington Palace shared an Instagram post featuring a throwback photo from 1988.
"As a society, we owe our wellbeing, and indeed our lives, to the men and women in our emergency services..."
Princess Diana, Prince William, and Prince Harry on October 28, 1991 in Niagra, Canada | Photo: Getty Images
"The first photograph in this post is of The Duke of Cambridge and The Duke of Sussex and their mother Diana, Princess of Wales, with their cousins Peter Phillips and Zara Tindall in the yard of the Old Fire Station :fire_engine: in the grounds of Sandringham House in 1988."
William and Harry wore matching blue coats and gold firefighter helmets as their mother watches.
Princess Diana Attends The "Gold Awards" At The Savoy in 1997 | Photo: Getty Images
The Instagram post is honoring 999 Day, a yearly occasion on the ninth hour of the ninth day of the ninth month which praises the work of police, fire, and emergency medical services in the United Kingdom, according to PEOPLE.
William said in a statement shared on Instagram:
"As a society, we owe our wellbeing, and indeed our lives, to the men and women in our emergency services who work tirelessly to protect us in some of the most difficult circumstances."
Prince William at the prizegiving after the inaugural King's Cup regatta on August 08, 2019 in Cowes, England | Photo: Getty Images
He added, "It is only fitting that we should recognize the vital role that they play, and pay tribute to the bravery and dedication of those who have made the ultimate sacrifice for their communities."
William also visited a group of firefighters at Harcombe House and promoted a new texting service through the Crisis Text Line in the United Kingdom, according to InStyle.
Prince Harry at Sportcampus Zuiderpark in May 2019 | Photo: Getty Images
A royal insider told Us Weekly that William and Harry meet up and spend the day together to honor their late mother on the anniversary of her death each year.
The royals were recollecting all the great times they had with the People's Princess over lunch or supper at Kensington Palace in London.
They likewise make it a point to keep their late mother's kind soul alive.
On August 31, 1997, Diana passed away in hospital after being injured in a car crash in a road tunnel in Paris, France.