The King and Queen hosted a glittering diplomatic reception at Buckingham Palace, with Camilla stepping out in the late Queen’s aquamarine and diamond tiara.

The Prince of Wales joined the monarch and consort for the grand white-tie affair on Tuesday night, but William was without the Princess of Wales, who is often a regular attendee at such events, at his side.

The King, in his knee breeches, and Queen at the Diplomatic Corps reception (Aaron Chown/PA)

Kate, who finished her chemotherapy treatment in the summer and is gradually returning to public duties as she recovers from cancer, is focusing on hosting her annual Christmas carol concert in Westminster Abbey in just over two weeks’ time.

Camilla was dressed in a blue velvet evening dress by Fiona Clare, and opted for Elizabeth II’s small aquamarine and diamond tiara as she gathered with some 900 guests at the Diplomatic Corps reception.

The delicate headwear – sometimes known as the aquamarine ribbon tiara – features five large aquamarines set in intricate ribbons of diamonds.

The Queen wore the late Queen’s small aquamarine tiara to the Diplomatic Corps reception on Tuesday evening (Aaron Chown/PA)

It is believed to be the first time Camilla has worn the jewellery.

The piece has been favoured in the past by the Duchess of Edinburgh who as the then-Countess of Wessex wore it to the gala dinner celebrating the Hereditary Grand Duke Guillaume of Luxembourg’s wedding in 2012, and at the wedding of Princess Madeleine of Sweden in 2013.