The Duchess of Cambridge wore the late Princess Diana's tiara to the annual Diplomatic Reception.

Duchess of Cambridge

Duchess of Cambridge

The 34-year-old royal - who is also known as Kate Middleton - attended the annual event, which was held at London's Buckingham Palace alongside her husband Prince William, his father Prince Charles and grandparents the Queen and Prince Philip, on Thursday night (08.12.16).

The brunette beauty stunned in a red Jenny Packham gown - the fashion designer who also created her unforgettable lace wedding gown - which she paired with a matching red clutch bag and her partner's late mother's diamond and pearl Cambridge Lover's Knot tiara to the bash.

This marks the fifth time Catherine has worn an item belonging to Diana, as the first time was on her wedding day five years ago.

Although the event was not the first time Catherine adorned a piece of what would have been her mother-in-law's headpiece, it marked the first ever occasion a photographer was given permission to photograph the Royal Family at such a private do.

Whilst Catherine stood out in her elegant rouge gown, Prince Charles' second wife the Duchess of Cornwall - who is also known as Camilla Parker Bowles - appeared to match the British monarch as the pair adorned ivory-coloured gowns with lace detailing, a blue sash and tiaras on top of their curly fair-coloured heads.

The Royal Family have taken to Twitter to showcase their eye-catching garments, and captioned the post: "Tonight The Queen and the Royal Family welcome the world's ambassadors to #BuckinghamPalace at the annual Diplomatic Reception (sic)."

Meanwhile, the 95-year-old Duke of Edinburgh showcased his vast amount of medals, which total up to 17, from the Second World War, as well as his Jubilee and Coronation medals to the ceremony.