The Princess of Wales stole the show at a lavish state banquet at Windsor Castle held in honour of the German president.
Kate, 43, stepped out in a stunning blue sparkling Jenny Packham gown for Wednesday evening's festivities alongside the Prince of Wales.
She wore Queen Victoria's Oriental Circlet tiara, a rarely seen piece of royal jewellery.
It was designed by German-born Prince Albert for his wife and features lotus flowers within eleven Mughal arches and 2,600 diamonds from Garrard in London.
Originally set with opals - that were later replaced by Queen Alexandra with Indian rubies - it became an 'heirloom of the Crown' upon Victoria's death in 1901, the Mail reported.
It was also worn frequently by the Queen Mother and only once by Queen Elizabeth in 2006, it is not believed to have been seen in public since - until last night.
King Charles and Queen Camilla posed for a group photo with the German president Frank-Walter Steinmeier and his wife Elke Budenbunder ahead of the state banquet getting underway on Wednesday evening.
Camilla wore a green lace evening gown by Fiona Clare and the Girls of Great Britain and Northern Ireland Tiara which was a favourite of the late Queen.
She paired her outfit with diamond earrings, an emerald and diamond necklace, and the Order of Germany sash.
The Christmassy state banquet was staged for the first time in modern royal history, with a magnificent 20ft Christmas tree adorning Windsor Castle's St George's Hall.
The president and his wife were feted at the glittering celebration, while their table was decorated in festive deep red poinsettias, bright red berries, and mini fir trees.
In his speech, King Charles spoke directly about the need for Western allies to stand up for Ukraine against Russia's invasion.
It comes as tensions between Europe and Russia appeared to intensity this week after Vladimir Putin accused Kyiv's European allies of sabotaging US-led efforts to end the war.
"It is 36 years since the fall of the Berlin Wall - a momentous event in human history,” Charles told his guests seated at the table.
"The tumultuous period of political, social and technological change that happened after that has tested our values. Many have found that unsettling and even frightening. Fear can lead to anger and resentment.
"But the United Kingdom and Germany are united in a continued belief in democracy, freedom and the rule of law."
The King spoke large parts of his speech in German and touched on a subject important to both nations - football.
The King said: "Football is of course another shared endeavour, and I am delighted to see so many of the footballing fraternity around the table with us here this evening.
"Of course, I use the word 'shared' in the broadest meaning of the word: there was, one has to admit, some element of truth in the famous description of football as a game where 11 people play 11 people, and then, in the end, the Germans win!"
The president also echoed the King's words about tensions in Europe, telling the guests: "We are working together to promote security and defence, side by side for a free, peaceful Europe, side by side in support of Ukraine."
Mr Steinmeier gave a speech and spoke about the royal family's connection with Germany and Christmas traditions.
He told the guests: "The atmosphere here is very familiar. After all, not all British people may be aware of this, but some of the best-loved Christmas traditions in this country originated in Germany.
"First and foremost the Christmas tree, the first one of which was displayed here in Windsor by Queen Charlotte in the year 1800 and which was soon to become a feature in many living rooms in the United Kingdom."
The modern British royal family has strong German links as Queen Victoria's mother was German and she married Prince Albert, German royalty.
Albert wad credited with popularising the Christmas tree, presenting large numbers to schools and Army barracks, and when a print was published in 1848 showing the royal family around the festive emblem, its use escalated throughout society.
German supermodel Claudia Schiffer and her filmmaker husband Sir Matthew Vaughn were among the guests on Wednesday evening.
Other famous names with German heritage or connections included movie-score composer Hans Zimmer, Strictly judge Motsi Mabuse, who lives in Germany, and children's book illustrator Axel Scheffler, known for bringing the much-loved character The Gruffalo to life in his drawings.
Ten members of the royal family gathered for the white tie banquet, the King and Queen, the Prince and Princess of Wales, the Duke and Duchess of Edinburgh, the Princess Royal and Vice Admiral Sir Tim Laurence, and the Duke and Duchess of Gloucester.
A Black Forest gateau cocktail was created especially for the occasion in tribute to the King and Queen's German visitors, with the idea of serving a new tipple personalised for each state banquet - a tradition started by Charles.
The drink blends cherry brandy with German chocolate, which has been clarified into a clear liqueur, and was served in a frosted glass with the rim dusted in chocolate and with a cherry as a garnish.
Such is the size of the towering Christmas tree, decorated in thousands of sparkling lights and green and gold ornaments, at the far end of the hall, that both the length of the mahogany dining table and the number of guests invited to the royal occasion had to be reduced.
One hundred and fifty-two people, eight less than the usual 160 at Windsor banquets, sat around the 45 metre-long table, which was two metres shorter than usual.
A Palace aide said: "It's shorter because of the whopper tree and the guest numbers have been reduced to 152 to make room. It looks magnificent."
They added it was the first time in living memory a Christmas tree had been on show for a state banquet in the UK.
Other guests include Prime Minister Sir Keir Starmer, who was seated next to Schiffer, whose placename read Lady Vaughn, her title thanks to the husband's knighthood.
German former football player Thomas Hitzlsperger, who played for Aston Villa, the team the Prince of Wales supports, and England Lioness Georgia Stanway were also invited.
The state visit was the first by a German leader to the UK in 27 years.
It was also the first time in 37 years that a British monarch has hosted three state visits in one year, with the last time in 1988 by Queen Elizabeth II.
The King, who is still being treated for cancer, hosted French president Emmanuel Macron in the summer and US president Donald Trump in September.
The president was seated between the King and Kate, while on the opposite side of the table, Ms Budenbender sat between Camilla and William.
The menu, written in French as is the custom, consisted of a tartlet of hot smoked trout with langoustines, quail eggs and shellfish sauce, followed by Windsor partridge supreme wrapped in puff pastry with confit cabbage and port sauce with crushed carrots and swede and an assortment of winter vegetables.
For dessert, there was a baked Alaska with blackberry, vanilla and raspberry ice creams, followed by coffee and petit fours.
The wine list diplomatically included a German white wine - Joh. Jos. Prum, Graacher Himmelreich, Spatlese, 2010 - and an English sparkling wine - Breaky Bottom, Cuvee Reynolds Stone, 2010, with a Veuve Clicquot Ponsardin, Vintage 2002 champagne.
A French red Chateau La Fleur-Petrus, Pomerol, 1995 was also chosen in a personal tribute to the president and his wife, in a nod to the year they married.
On the table were 158 candles, 760 glasses and 152 spoons, 320 knives and 320 forks.
The silver gilt Grand Service used consisted of 4,000 pieces and was commissioned by the extravagant George IV as the Prince of Wales.
Household staff spent the last week setting up the antique table.
The seasonal flowers were handpicked from the gardens at Windsor Castle, Buckingham Palace and the Saville Garden in Windsor Great Park - with the poinsettias, popular as Christmas houseplants, coming from the Windsor greenhouses.
Afterwards, flowers that could not be reused were donated to Floral Angels, a charity of which the Queen is patron, and delivered to hospices, elderly care homes and shelters.
Music played during the banquet by the Duchess of Edinburgh's String Orchestra, included a repertoire of classical German and popular music, with Zimmer's film score tracks Gladiator, The Pacific, Pirates Of The Caribbean: At World's End.
Strauss' Blue Danube Waltzes, Mendelssohn's Canzonetta, and Handel's Five Pieces from Music for Royal Fireworks also featured, along with Adele's Skyfall and a Beatles medley.
