Catherine, Princess of Wales paid tribute to Princess Diana with her outfit at King Charles' historic Trooping the Colour

The jewels were a gift from Catherine's husband Prince William, 40, who also gifted her his mother's sapphire engagement ring when he proposed in 2010.

They were originally given to Diana as a wedding gift as part of a suite of jewels from Crown Prince Fahd of Saudi Arabia, and in a special "letter of wishes" included in her will, Princess Diana said: "I would like to allocate all my jewellery to the share to be held by my sons, so that their wives may, in due course, have it or use it. I leave the exact division of the jewellery to your discretion."

Catherine wore an emerald green dress paired with a Philip Treacy hat - 36 of which were sported at her and William's 2001 wedding.

William dressed in his red military uniform, which he teamed with a traditional bearskin hat and medals on his chest for the big day.

His horse Darby was a gift to the late Queen, who died in September aged 96, from the Royal Canadian Mounted Police - and led the emotional funeral procession for his grandmother last year.

Trooping the Colour commemorates 74-year-old Charles' official, but not real, birthday and is held every year.

It dates back to Charles II in the 17th century when regiment colours trooped in front of soldiers so they could recognise their unit in battle.

Charles, who was crowned with Camilla on 6 May, beamed as he and a set of senior working royals waved to crowds from the balcony of Buckingham Palace after the Red Arrows led a flypast tribute to mark the Trooping the Colour.

Three Hercules aircrafts roared by, with George and Louis visibly stunned by the planes.

Making up the initials CR, 18 typhoons made their way through the skies of London.

The stunning red arrows then painted the sky red, white and blue as fans below the palace balcony cheered with the royal family.

Beside Charles on the balcony stood William, the Princess Royal and the Duke of Edinburgh.

When the clock struck 11am, Charles received a salute before the National Anthem was played in the Horse Guards Parade.

The event featured around 1,500 soldiers in total with hundreds of Guardsmen lined up on the parade ground waiting to be inspected by the King.

Police officers and paramedics had to assist a female solider who fainted during the procession.

The Duke and Duchess of Sussex did not attend the event.

In another sign Charles is sticking to his reported plan for a more "slimmed down" monarchy, missing from this year's balcony was the Duke and Duchess of Edinburgh's children, James, Earl of Wessex and Lady Louise Windsor.

Also absent from Trooping the Colour this year was Princess Alexandra, 86, a cousin of the late Queen.