The Duchess in Lover's Knot Tiara for Diplomatic Reception!

Following a Christmas party with RAF families at the Orangery, the Duchess changed from her festive ensemble into a gown and jewels for the annual Diplomatic Reception at Buckingham Palace.

The Duchess arriving.

It was a rainy evening in London.

In a major departure from previous years, a pool photographer was invited inside to take photos. It's a wonderful surprise and hopefully the beginning of a new tradition.

William and Kate joined Her Majesty the Queen, Prince Charles and the Duchess of Cornwall for the white-tie event.

The Queen wore her Girls of Great Britain and Ireland tiara.

The Duchess of Cornwall selected the Greville tiara for the night.

There are over 170 foreign missions accredited to the court of St James's in London (St James's Palace is still the senior palace and official residence of the sovereign).

Each year Her Majesty throws a reception in their honour and members of the Royal family in attendance make a point of meeting with each one.

Guests were welcomed to the palace ballroom. At 36.6m long, 18m wide and 13.5m high, the ballroom is the largest multi-purpose room in Buckingham Palace. It was opened in 1856 with a ball to celebrate the end of the Crimean War. It is used by the Queen for State banquets.

The Duchess mingling with guests.

Kate was every inch a princess in a shimmering bespoke Jenny Packham gown (with thanks to Heaven). The delicate beading and sheer overlay add delicate touches to the sweeping gown. Jenny Packham remains the Queen of evening wear for Kate. Another gorgeous design.

A closer look at the detailing.

The Duchess wore her signature Lover's Knot tiara tonight.

The tiara, which is steeped in royal history and is so closely associated with William's mother, looks beautiful on Kate. It's a stunning piece and one I expect we'll see the Duchess wearing throughout her life. The tiara features elements of the Gothic Revival style. The circle of the Lover's Knot is made up of a lower semi-circular band, set with a row of brilliant cut diamonds. Where two adjacent arches meet, a pillar-like structure is formed that rises up and ends in a round diamond, forming a diamond spike. There are nineteen diamond spikes of this nature and the size gradually decreases from the centre towards both ends.

Kate last sported the tiara for the Dutch State banquet in October.

The Duchess wore Diana's Collingwood pearl earrings once again.

The Duchess wore her Royal Family Order. Kate was awarded the RFO last year; it's made of glass.

A closer look at Kate's Jenny Packham clutch and shimmering bracelet.

If you're just joining us, click here to read today's earlier post.

We also have word on another pre-Christmas engagement for the Cambridges next week. Kensington Palace confirms:

'The Duke and Duchess of Cambridge will visit Evelina London Children’s Hospital and homeless resource centre The Passage on Tuesday 11th December.

The Duke and Duchess will meet a number of children receiving care at the hospital, and will hear more from staff and parents about Evelina London’s life changing care and support for families. Their Royal Highnesses will then join some of the children as they take part in a number of Christmas-themed activities, before joining celebrations to mark the 150th anniversary of the founding of the hospital.

The Duke and Duchess will then travel to The Passage, where they will hear from frontline workers about some of the challenges relating to street homelessness, including drug addiction and mental health issues. Their Royal Highnesses will also meet a number of The Passage’s service users as they join an arts and crafts workshop to prepare cards and gifts ahead of centre’s Christmas party the following week.'

Tomorrow, William and Kate will fly to RAF Akrotiri in Cyprus to meet with serving personnel, families living on the base, wider station personnel and members of the local community.