The Princess of Wales wore the popular Lotus Flower Tiara for tonight’s diplomatic reception. Below, the Prince and Princess on their way to the reception. (How fun is the expression on the woman’s face reflected in the window?)
Below, Camilla, Queen Consort. 
This is the first time King Charles and the Queen Consort have hosted the event. As many as 2000 members of the diplomatic corps are welcomed to Buckingham Palace for the reception. 
The Prince and Princess. 
More from The Daily Mail’s coverage.
The event at the Palace is the first Diplomatic Corps reception of the King’s reign, and the monarch, his consort Camilla, eldest son and heir to the throne William and daughter-in-law Kate, a future queen, welcomed foreign ambassadors to the grand occasion in the royal residence’s state rooms.
The late Queen was set to host the white tie gathering in March this year at Windsor Castle, but it was postponed due to Russian’s invasion of Ukraine.
It is usually held every December, but there were no receptions in 2020 and 2021 due to the Covid pandemic. The reception traditionally includes a buffet supper and dancing.
The most recent reception for the Diplomatic Corps was hosted by Queen Elizabeth II at Buckingham Palace in December 2019.
Now for our look at what the two royal women wore for the reception, starting with Camilla, Queen Consort. 
She was in a gown by Anna Valentine, per this Hello magazine story. She accessorized with stunning sapphire and diamond jewelry: the George VI sapphire necklace, a coordinating tiara, and earrings. The Court Jeweller notes, “The Queen received the sapphires from her father as a wedding present in 1947, hence the set’s usual name.” More about the tiara from The Royal Order of Splendor.
This tiara traces back to Princess Louise of Belgium (1858-1924), who was the daughter of King Leopold II and the wife of Prince Ferdinand Philipp of Saxe-Coburg and Gotha. When you look at the current tiara, you can indeed detect a bit of pointiness – the tell-tale look of a converted necklace instead of something designed specifically to be a tiara.
Below is a closer look. 
Moving now to the Princess of Wales, who chose a Jenny Packham design for tonight’s function. 
The ‘Elodie gown is from the designer’s pre-fall 2019 collection and features a floral motif, round neckline, semi-sheer bodice, and extended keyhole back. Many thanks to UFO No More for their ID of this piece. 
A closer look at the gown shows the zippers at the wrist and the intricate beading and sequin work embellishing the dress. 
As mentioned above, tonight, the Princess chose the Lotus Flower Tiara, also called the Queen Mother’s Papyrus Tiara.
This is the third time the Princess has worn the tiara. We first saw her wearing it to the 2013 diplomatic reception. We had better pictures when it was worn almost two years later for the China state dinner.
A closer look. 
More about the piece from The Court Jeweller:
The first royal wearer of this tiara, which takes its name from the lotus flower (or papyrus leaf) elements that dominate the piece, was the Queen Mum. She took a page out of her mother-in-law’s book when creating the sparkler: it was made from a necklace that she received as a wedding gift in 1923. The necklace, which was made of diamonds and pearls and featured meander and festoon designs, was given to her by her husband, the future George VI, who had purchased it from Garrard.
Even so, Elizabeth decided she’d rather dismantle it and reuse the gems elsewhere. Only six months after she received it, Garrard broke up the necklace and used the diamonds and pearls to create this tiara.
Below, the Queen Mother wearing the piece. The Royal Order of Splendor writes, “The then-Duchess of York wore it in the fashionable bandeau style across her forehead, but it is equipped to be worn in traditional style at the crown of the head as well.”
The Court Jeweller reports, “Margaret received the tiara from her mother in 1959, just before she married Antony Armstrong-Jones. Along with the Poltimore, it became one of her most frequently worn tiaras.” Below, Princess Margaret wearing the piece.
The Princess wore Queen Elizabeth’s Diamond Frame Earrings, the art deco Bentley and Skinner brooch first seen at this year’s Remembrance Sunday service, and Queen Elizabeth II’s Royal Family Order, personally bestowed by The Queen to female members of the Royal Family.
Below, the late Queen wearing the earrings for the State Opening of Parliament in 2012 and the Duchess wearing them for a Place2Be engagement in 2016.
The Princess also wore the sash, badge, and Maltese Cross of the Royal Victorian Order, also awarded to her by the late Queen. (They are shown below as worn on another occasion.)
Below, a look at several of the more recent diplomatic reception ensembles worn by the Princess of Wales. The 2016 and 2018 gowns are by Jenny Packham, while the 2019 style is an Alexander McQueen design. 
Larissa
Thursday 22nd of December 2022
So refreshing to see Kate in a different tiara, even if it isn't new to us. This is a stunning gown, and looking at it in the side-by-side with other diplomatic receptions, I would rank it among the best along with the other red Jenny Packham. I appreciate that the beadwork and lace are what make the dress interesting, and the style remains sleek and classic. I also love the added volume in Kate's hair that makes the tiara stand out. How great to see two tiara functions in such a short amount of time after so many years of being deprived of them!
Pamela
Tuesday 13th of December 2022
I love this whole look!! Is it just me, but is Kate reminding anyone else of Crown Princess Mary of Denmark!! Mary often wears her hair in the same high-crown volume with a tiara. While I love Kate’s spectacular chignons, it was a fun dash of variety to see the sleek look paired with the Lotus Flower tiara. Well done, Kate!!!
Christa
Sunday 11th of December 2022
Gorgeous! @Susan, how are royal orders attached to the gowns? Is it a magnet? That gorgeous dress with the intricate mesh and beading would be ruined with pins, wouldn't it? Thanks!
Caroline A.
Monday 19th of December 2022
@Christa, I think the Royal Family Orders are suspended from the ribbons and the ribbon itself it pinned to the gown. The ribbon supports the weight of the Royal Family Order. The following video is interesting; it shows how Royal Orders are attached to a uniform by being suspended from what appear to be loops made of thread that are sewn into the garment. This might be how the heavy Orders are worn without damaging the delicate fabric of the dress, but I suspect that there would need to be some kind of heavier material/backing sewn into the dress so that the dress wouldn’t sag, as you say.
https://www.sothebys.com/en/videos/get-the-royal-wedding-look
Caroline A.
Pamela
Wednesday 14th of December 2022
@Christa, I have wondered this too! Perhaps they tailor something into the dress to support the piece from behind? Or maybe they sew the heavier pieces onto the dress for the one wearing? But I agree with you; I can’t believe they just stick giant heavy pins into a dress made of such thin delicate fabric that cost thousands of dollars! There has to be some sort of heavier fabric behind the beads and lace to support. Another thought I always had was that a heavy brooch pinned to your shoulder, like QEII always wore, would make your neckline sag on a silk dress, or even make your dress fall too far forward when you bend down to get out of the car. If I ever meet Angela Kelly, maybe I’d get some answers!!!!
Diane
Saturday 10th of December 2022
I don't know enough about jewelry, especially tiaras, to understand this quote and know what to look for as far as pointiness, can someone please explain to me? Thank you!
"When you look at the current tiara, you can indeed detect a bit of pointiness – the tell-tale look of a converted necklace instead of something designed specifically to be a tiara."
Caroline A.
Tuesday 13th of December 2022
@Diane, Further to my lengthy reply to you, after I had posted it I found the following link which has a much clearer photograph of Princess Louise of Belgium wearing the necklace that later became the tiara. This time it is worn around the neck, rather than being pinned to the neckline of a dress.
https://www.thenaturalsapphirecompany.com/blog/the-top-10-sapphire-tiaras-of-all-time
Caroline A.
Caroline A.
Tuesday 13th of December 2022
@Diane, your’re very welcome! I love the way we can communicate and share information on What Kate Wore. At first I, too, thought it was just the large central front part of the tiara that Princess Louise of Belgium wore pinned to her dress in the photo, but when I re-read the article, it didn’t mention that and seemed to be saying that it was the whole thing that was pinned to the neckline of the dress. That is, it wasn’t just a brooch, (the central pointy bit), but a necklace, which was subsequently worn as a tiara. If you look closely at the grainy photo, it is possible to discern the other, smaller, individual pointy bits further along the dress on either side of the central pointy bit. It’s a bit easier to see that if you turn the device you are using upside down, I found. The necklace would have been to been altered to form a tiara, e.g. by mounting it on a circular frame, but I think it’s essentially the same piece of jewellery as the necklace.
You, and other readers, may be interested to see the information in the following link from the blog entitled From Her Majesty’s Jewel Vault: It includes a photo from Angela Kelly’s book Dressing the Queen: the Jubilee Wardrobe, which shows the sapphires from The George VI and Modern Sapphire Set in the tray in which they were transported to Queen Elizabeth II for use. The article also states: “They are accompanied by the regular diamond evening watch and three options for sapphire rings to wear”. The idea of having a “regular” diamond evening watch amused me :-) The link to the watch explains that Queen Elizabeth II had several diamond evening watches, but this watch was her favourite at the time.
The second link below, this time from The Court Jeweller blog, confirms that the tiara was fashioned from a necklace by attaching it to a frame. So, it was the whole tiara that was worn as a necklace by Princess Louise, not just the middle pointy bit.
http://queensjewelvault.blogspot.com/2012/11/the-george-vi-and-modern-sapphire-set.html
https://www.thecourtjeweller.com/2016/09/the-belgian-sapphire-tiara.html
Caroline A.
Diane
Sunday 11th of December 2022
@Caroline A., thank you so much for the clarification. I went to the article you gave a link for and now it makes a bit more sense. So the large, center front part of the tiara the Queen Consort is wearing started as either a necklace or dress ornament? I can visualize that, especially after seeing the photo in the linked article, but it still doesn't look particularly pointy to me, just a bit higher than the rest of the tiara. But comparing it to the other tiaras shown, I see the others are more uniform in height. Clearly I know even less than I realized about tiaras! But it is very interesting. Thank you so much.
Caroline A.
Sunday 11th of December 2022
@Diane, according to the article in the link below, for which Susan provided a link also, the George VI Sapphire Tiara started out as “either a necklace or a dress ornament”, not as a tiara, and was worn by Princess Louise of Belgium pinned to her dress (with the large sapphire in the middle pointing downwards). In the article there is a photo of a Princess Louise wearing it. In the current tiara, the large sapphire points upwards, giving it a “pointy” appearance, with the result that it is easy for people who know about tiaras to deduce that it didn’t start out as a tiara. I’m no expert, but when I myself first saw it, (and didn’t realise then that it was essentially upside down), I thought it looked a bit strange, as I didn’t like the pointy bit in the middle, but I rather like it now that I have become used to seeing it.
http://orderofsplendor.blogspot.com/2012/11/tiara-thursday-modern-sapphire-tiara.html
Caroline A.
Caroline A.
Saturday 10th of December 2022
The strange thing about the woman in the photo of The Prince and Princess of Wales in the car is that she bears a resemblance to Catherine as a teenager, at least to my mind. See the photo of Catherine goofing around in 1999 in the link below.
https://www.goodhousekeeping.com/life/entertainment/g3138/kate-middleton-life-in-pictures/
Caroline A.