The Trump dynasty mingled with the royal family at the lavish state banquet, where industry chiefs rather than Hollywood stars gathered to honour US President Donald Trump.
But who sat next to whom? Who wore what? Who said what? And what was on the menu?
Here is a behind-the-scenes look at the inside story of when the Royal Family hosted the Trumps.
Where did the guests sit?
As is tradition, the Queen, who does not have her own place card, was at the head of the table, with the Prince of Wales on her left and Trump on her right.
Joining Trump and First Lady Melania at the white tie and tiara event were four of Trump's five children - Ivanka Trump, with her husband Jared Kushner, Donald Trump Jr, Eric Trump and his wife Lara, and Tiffany Trump.
Sixteen members of the royal family were also at the dinner - the Queen, the Prince of Wales, the Duchess of Cornwall, the Duke and Duchess of Cambridge, the Duke of York, the Earl and Countess of Wessex, the Princess Royal, Vice Admiral Sir Tim Laurence, the Duke and Duchess of Gloucester, the Duke of Kent, Prince and Princess Michael of Kent and Princess Alexandra.
The Duke of Sussex, who was at the private lunch earlier, was noticeably absent, as was the Duchess of Sussex who is on maternity leave, looking after their four-week-old son Archie.
Charles, who had tea with Trump earlier on Monday, was seated next to Melania Trump, while Camilla was on the other side of the president and next to US ambassador Woody Johnson.
William sat between the Prime Minister Theresa May and Mr Johnson's wife Suzanne Ircha. Kate was seated between US secretary of the treasury Steven Mnuchin and the Lord Mayor of London Peter Estlin.
The president's daughter and adviser Ivanka sat between the Countess of Wessex and International Trade Secretary Liam Fox, while Ivanka's husband Mr Kushner, a senior adviser to Trump, had the Princess Royal on his right and Mark Carney, governor of the Bank of England, on his left.
Former US president Barack Obama's state banquet in 2011 was sprinkled with Hollywood stardust, with a guest list including actor Tom Hanks, actress Helena Bonham Carter and director Tim Burton.
But Trump's grand occasion was more trade and business than show business.
Among the captains of industry invited were Swedish businessman and chairman of AstraZeneca Leif Johansson, chairman of BP Helge Lund, Balfour Beatty chief executive Leo Quinn, GlaxoSmithKline boss Emma Walmsley, Universal Music Group chairman Sir Lucian Grainge and Royal Dutch Shell chief executive Ben van Beurden, as well as Metropolitan Police Commissioner Cressida Dick.
Politicians at the event included Theresa May and her husband Philip , Cabinet Office minister and Chancellor of the Duchy of Lancaster David Lidington, Chancellor Philip Hammond, Foreign Secretary Jeremy Hunt, Defence Secretary Penny Mordaunt, Fox, Environment Secretary Michael Gove, Leader of the House of Lords Baroness Evans and Europe and Americas minister Sir Alan Duncan.
Tiffany Trump was seated between HSBC chairman Mark Tucker and the Queen's top aide, her private secretary Edward Young, while Lara Trump, Trump's daughter-in-law, was between Lord Hague and van Beurden.
The decor and the displays
In the Buckingham Palace ballroom with its six glittering chandeliers, the vast white-clothed horse shoe-shaped table was laden with George IV's silver gilt Grand Service dinner set.
Small white place cards embossed with a golden royal crest and edged in gold were at each setting, to show where the 170 guests were seated.
Twenty three elaborate floral displays of dark pink peonies, lilac stocks and pale pink roses adorned the table, along with large seven-branch state candelabrum and the elaborate soup tureen which was once used to serve George IV his favourite turtle soup.
The Queen earlier inspected the ballroom in person to make sure everything was perfect for her visitors.
Tablecloths and napkins - folded in the shape of a Dutch bonnet - cruet sets and six glasses at each setting - for water, a champagne toast, red and white wines, a dessert wine and port - were all carefully in place - although teetotal Trump did not sample the wines on offer.
A special red velvet cushion was ready on Charles' chair to help ease his back pain.
Every place setting was 18 inches apart - with measuring sticks used to ensure absolute precision.
Preparations for the banquet began six months before the event and it took palace staff four days to lay the table.
Nineteen stations were set up around the table, each manned by four staff - a page, footman, under butler and a wine butler - who use a traffic light system to co-ordinate the serving of courses.
The event operated with military precision. It took staff one hour and 15 minutes to serve the banquet and about one hour and 30 minutes to clear away afterwards.
Donald Trump dined on a menu of Windsor lamb and strawberry sable at the Queen's state banquet.
In the opulent Buckingham Palace ballroom, the guests were treated to steamed fillet of halibut with watercress mousse, asparagus spears and chervil sauce.
This was followed by saddle of new season Windsor lamb, with herb stuffing, spring vegetables and port sauce.
The menu will have been chosen from four possible alternatives presented to the Queen by royal chefs.
Preparations in the kitchens of Buckingham Palace begin as close to the event as possible - with every dish handmade from scratch.
Trump is known to have a sweet tooth so is likely to have enjoyed the pudding - strawberry sable with lemon verbena cream - made of crisp biscuits, smooth pastry cream and fresh strawberries.
Here is the menu:
• Steamed fillet of halibut with watercress mousse, asparagus spears and chervil sauce
• Saddle of new season Windsor lamb with herb stuffing, spring vegetables, port sauce
• Strawberry sable with lemon verbena cream
• Selection of assorted fresh fruits
• Coffee and petit fours
The banquet in numbers
Here's a look at the Buckingham Palace state banquet for US President Donald Trump in numbers:
75 - Minutes it takes to serve the banquet
90 - Minutes it takes to clear away afterwards
4 - Days taken to lay the table
6 - Glasses at each place setting
170 - Guests
8 - Members of the Trump family at the dinner - Trump, First Lady Melania, Ivanka Trump, her husband Jared Kushner, Donald Trump Jr, Eric Trump and his wife Lara, and Tiffany Trump.
16 - Members of the royal family present
18 - Inches between each place setting
23 - Floral displays around the banquet table
75 - Length of the table in feet
100 - Ivory candles in the ballroom
1020 - Glasses used
£1400 - Cost of a bottle of Chateau Lafite Rothschild 1900, 1er Cru Classe, Pauillac which is among the drinks being served
4000 - Pieces in the silver gilt George IV's Grand Service dinner set, including 14 tureens, 20 sauce tureens, 140 dishes, 288 dinner plates, 118 salts, 12 ice pails, 12 mirrored plateaux, 58 dessert stands and centrepieces, and 107 candelabras
The Queen's state banquet guests washed down their lavish dinner with wines costing from £38 up to £1400, but not US President Donald Trump - who is teetotal.
The food and drink served to diners at royal events usually features produce from the Queen's estate, and those invited to the Buckingham Palace banquet in honour of the US president were served a 2014 English sparkling wine from Windsor Great Park, priced at about £37.99.
Red wine lovers quaffed Chateau Lafite-Rothschild 1990 - 1er cru classe Pauillac, costing up to £1,395 a bottle, for those with deep pockets.
Trump is said to have never drunk and encouraged his children to abstain from alcohol.
Other wines served included another sparkling wine from the UK - the Hambledon Classic Cuvee Rose NV costing £34.95 and the white burgundy Chassagne Montrachet 1er Cru Morgeot Louis Jadot 2014 priced at about £75.
The Duchess of Cambridge wore her sash and star of the Dame Grand Cross of the Royal Victorian Order for the first time.
Kate stepped out in a ruffled white Alexander McQueen gown, wearing the dark blue sash edged in pink over her right shoulder and the star on the left side of her waist, as is the custom.
The duchess was awarded the prestigious honour by the Queen in April on the day she celebrated her eighth wedding anniversary.
It was given in recognition of her efforts supporting the head of state since marrying into the royal family in 2011.
Her tiara was her go-to choice for banquets - the diamond and pearl Lover's Knot, which was a favourite of the late Diana, Princess of Wales.
Her sapphire and diamond earrings were loaned by the Queen.
She also wore her Royal Family Order, a portrait of the Queen on a yellow ribbon.
White appeared to be the theme for gowns on Monday evening, with the Queen dressed in a state evening gown with crystal centred daisies by Angela Kelly, with a Burmese ruby and diamond tiara and a ruby and diamond necklace.
First Lady Melania Trump also went for a shade of white, wearing a Dior Haute Couture ivory silk crepe gown with silk tulle details.
The Duchess of Cornwall wore a cream embroidered evening gown by Bruce Oldfield, as well as the diamond boucheron tiara, a pearl and rose topaz choker and diamond earrings.
Donald Trump's younger daughter Tiffany Trump was dressed in a dark red off-the-shoulder velvet gown and wore her hair down.
She also opted for long white gloves like her stepmother Melania.
Eric Trump, in white tie and tails, was seen smiling with his wife Lara, who wore a black and white patterned gown, also with long white gloves, as they made their way to the grand ballroom.