Catherine, Duchess of Cambridge, joins the Queen at centuries-old royal ceremony

The royal women wowed onlookers at a centuries-old service at Windsor, amid new reports that fuel speculation of a deepening rift between Prince William and Prince Harry and their wives.

Catherine, Duchess of Cambridge, stunned in all white as she joined the Queen and European royals at the Knights of the Garter ceremony.

The Duchess of Cambridge dazzled in a £250 ($A450) dress at the annual service at Windsor.

The 37-year-old wore a 1950s ivory coat dress with cropped jacket “panels” with fine black lace by Catherine Walker, reports the Sun.

She was joined by Queen Letizia of Spain, Queen Maxima of the Netherlands and Camilla, the Duchess of Cornwall for the annual service.

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Netherlands' Queen Maxima and Britain's Catherine, Duchess of Cambridge. Picture: Steve Parsons / POOL / AFP

Queen Letizia of Spain, Camilla, the Duchess of Cornwall and Catherine, Duchess of Cambridge at the Order of the Garter Service. Picture: Getty Images

The Duchess wore a $450 dress to the service. Picture: Ben Stansall/AFP

They appeared all smiles as they supported their husbands, King Felipe VI of Spain and King Willem-Alexander of the Netherlands as they were officially invested Knights of the Garter by her Majesty.

CHARITY SPLIT FUELS RUMOURS OF DEEPENING RIFT

Meanwhile, an insider has claimed Prince Harry and Meghan Markle are planning to split from a charity they set up with Prince William and Kate Middleton.

The Royal Foundation will be divided between the Sussexes and Cambridges as the couples focus on their own separate charitable endeavours according to recent reports.

According to The Sunday Times, the “decision is expected to be formally announced at a board meeting on Wednesday.”

The young royals at the first annual Royal Foundation forum. Picture: Getty Images

What’s more, a charity insider told The Mirror: “At the start of last year, the plan was that all four would work together and I really believed in them as the power of four.”

In February 2018, the “Fab Four” then attended the Royal Foundation forum together for what looks like the first and only time.

The insider added: “The forum was going to be an annual event and last year’s was supposed to be the first of many. It’s very sad it’s going to end like this.”

QUEEN STEPS OUT IN CEREMONIAL DRESS

The Queen and the Garter Knights wore their blue velvet robes and black velvet hats with white plumes at today’s event.

The Queen was joined by the Prince of Wales, the Duke of Cambridge and other senior royals in St George’s Chapel at Windsor Castle at the service.

The Queen was all smiles. Picture: AFP

The Order of the Garter is a 700-year-old tradition that was founded by Edward III in 1348.

It recognises the contributions of public service from those lucky to be honoured by the Queen — typically Lords and Ladies in the UK.

The Order has a limit of 24 members, excluding The Queen and the Prince of Wales. Foreign royals have been given “Stranger Knight” status since 1813.

Queen Maxima and Kate, Duchess of Cambridge. Picture: Getty Images

“Stranger Knight” is a second order bestowed upon foreign royals.

In the past a controversial recipient was Kaiser Wilhelm of Germany before World War I.

The last time a “Stranger Knight” was invested was King Harald of Norway in 2001.

Royals often keep the honour during their reign and then pass the title to their successor.

Queen Letizia of Spain. Picture: Getty Images

Sophie, Countess of Wessex. Picture: Getty Images

Other foreign royals who are currently “Stranger Knights” are Queen Margrethe of Denmark, King Carl Gustaf of Sweden, former King Juan Carlos of Spain, Princess Beatrix of the Netherlands, King Harald of Norway and former Emperor Akihito of Japan.

Prince William and Prince Charles leave the Order of the Garter Service. Picture: Getty Images

Knights of the Garter are chosen personally by the Queen for helping her either in her personal life or by contributing in a particular way to national life.

The appointment is considered a gift and the Queen makes her decision without consulting ministers.

Prince Charles shares a joke with his mother. Picture: AP

Two official appointments were made today as Lady Companion, Lady Mary Peters, and Knight Companion, Robert Gascoyne-Cecil the Marquess of Salisbury were invested by the Queen.

Soldiers at the ceremony. Pictures: Getty Images

Lady Mary is a former Lord Lieutenant of Belfast and the Marquess of Salisbury is a former leader of the House of Lords.

Hundreds of spectators saw the Garter Knights walking through the grounds of Windsor Castle.

Princess Anne at the ceremony. Picture: Getty Images

The royal women made sure to dazzle during today’s historical engagement.

The Spanish royal wore a £250 ($A450) dress by Spanish label Cherubina as her Dutch counterpart wore a pale pink dress.

The Queen with King Willem-Alexander of the Netherlands and his wife, Queen Maxima. Picture: AP

The ceremony also marked what is believed to be the second time Kate and Queen Letizia met.

Two royals who were missing today were Prince Harry and his wife Meghan.

The Duke of Sussex has not been invested himself, but he attended an event today about continuing his mum Princess Diana’s work on ridding landmines from Angola.

The Queen and Prince Charles. Picture: Getty Images

This story was originally published in The Sun and is reprinted with permission.