Duchess of Cambridge Pays Tribute to Princess Diana During Trooping the Colour

The royal family kicked off four days of celebrations to mark Queen Elizabeth's Platinum Jubilee with the annual Trooping the Colour procession and balcony viewing.

However, it was Catherine, Duchess of Cambridge, who stole the show with her subtle tribute to her late mother-in-law, Princess Diana.

While the entire royal family coordinated in shades of blue, Catherine opted for a white version of her favourite Alexander McQueen coat dress, paired with a navy Philip Treacy hat.

She also wore the same coat dress last summer as she joined senior royals at the Eden Project for G7 reception.

Catherine is a huge fan of the British brand, sporting designs on several occasions, most famously to her wedding in 2011.

Today, she added a Philip Treacy hat to the ensemble and paid a sweet tribute to Princess Diana by wearing her late mother-in-law's earrings and necklace.

The diamond and sapphire earrings from Princess Diana's collection are believed to be a present from William before their wedding.

Catherine also appeared to sport a necklace from Diana's collection, which is strikingly similar to a pair of earrings worn by Princess Diana, known as the Saudi Suite, a wedding present from Crown Prince Fayed.

Diana famously loved sapphires and wore the entire set to a Brisbane state reception in 1983 but also experimented with each item separately.

The earrings contained detachable sapphire drops, which Diana removed before wearing the resultant chunky studs, each surrounded by 10 round diamonds to mark Harry's birthday in 1985.

William gave them to Catherine after their engagement in 2010, and she refashioned them into modest drop earrings but wore them in their original state today.

Catherine tied her hair back into a sleek plaited bun and showed off her natural beauty with a simple make-up look, pairing a light layer of foundation with smoky brown eyes and pink lipstick.

Her accessories included the Philip Treacy hat, the favourite Milner of royal circles, and Princess Diana's earrings and necklace.

Of course, Catherine wasn't the only royal making references to the past.

She dressed her youngest son, Prince Louis, in the same nautical sailor suit Prince William wore to Trooping the Colour when he was just 2 years old.

Elder children Prince George and Princess Charlotte matched the theme in a blue suit and periwinkle dress, respectively.

Queen Elizabeth wore a powder blue coat with white embellishments and a coordinated hat, while Prince William, Prince Charles and Prince Anne all sported their military uniforms.

However, it was Catherine's subtle nod to Princess Diana's continued influence over the royal family that was apparent to followers of the clan.

Her Royal Highness has previously sported the earrings but removed the top circular sapphires.

Catherine was first photographed in the elegant single drop design in an official portrait at Clarence House on June 3, 2011.

Today, she paid tribute to her late mother-in-law, who passed away more than two decades ago, by wearing her precious jewels.

The yearly event honours not only Her Majesty's 70 years on the throne but also her birthday.

The celebration kicked off Thursday with the annual Trooping the Colour procession and balcony viewing.

The entire royal family, including the Queen, Catherine's three children and Camilla, Duchess of Cornwall, coordinated in shades of blue.

Catherine's sweet tribute to Princess Diana was a touching moment during the celebrations.

The Duchess of Cambridge's love for her late mother-in-law is evident, and her choice to wear her precious jewels shows that Princess Diana's legacy lives on within the royal family.