If a dress code memo was discreetly circulated, these ladies certainly received it.

Queen Elizabeth, First Lady Melania Trump and the Duchesses of Cambridge and Cornwall all looked lovely at a lavish Buckingham Palace banquet on Monday night, capping off President Donald Trump’s first busy day in London upon his official state visit to the U.K.

Notably, FLOTUS and the three royal women all wore white gowns for the high-powered occasion – a style moment that one expert argues was more likely coincidental than coordinated.

From left, US President Donald Trump, Britain's Queen Elizabeth II, first lady Melania Trump, Prince Charles and Camilla, the Duchess of Cornwall pose for the media ahead of the State Banquet at Buckingham Palace in London, Monday, June 3, 2019. (AP Photo/Alastair Grant, Pool)

From left, US President Donald Trump, Britain's Queen Elizabeth II, first lady Melania Trump, Prince Charles and Camilla, the Duchess of Cornwall pose for the media ahead of the State Banquet at Buckingham Palace in London, Monday, June 3, 2019. (AP Photo/Alastair Grant, Pool)

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"I agree it would appear as if there was an agreement that all the royal women would wear white and Melania was advised to do the same, but I really think it is a coincidence," British bridal designer Caroline Castigliano told Marie Claire.

Kate, the Duchess of Cambridge and United States Secretary of the Treasury, Steven Mnuchin arrive through the East Gallery ahead of the State Banquet at Buckingham Palace in London, Monday, June 3, 2019. (Victoria Jones/Pool Photo via AP)

Kate, the Duchess of Cambridge and United States Secretary of the Treasury, Steven Mnuchin arrive through the East Gallery ahead of the State Banquet at Buckingham Palace in London, Monday, June 3, 2019. (Victoria Jones/Pool Photo via AP)

"The royals often wear white to the state banquets and I wonder if this is partly to show off their sashes,” Castigliano dished. “Kate wore her blue sash tonight for the first time that symbolizes her role as a member of the Royal Victorian Order.”

The Duchess of Cambridge subtly honored her late mother-in-law Princess Diana at the 150-person soiree, sporting the Lover’s Knot tiara, which was known to be one of the royal’s favorite pieces.

US President Donald Trump, left and Queen Elizabeth II make a toast during the State Banquet at Buckingham Palace, in London, Monday, June 3, 2019. (Dominic Lipinski/Pool Photo via AP)

US President Donald Trump, left and Queen Elizabeth II make a toast during the State Banquet at Buckingham Palace, in London, Monday, June 3, 2019. (Dominic Lipinski/Pool Photo via AP)

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Traditional white-tie dress code – like that instated for the dinner – mandates that women wear floor-length evening gowns with the option of adding long gloves, according to the Emily Post Institute. Likewise, men are advised to wear black tailcoats with a white bowtie and vest, among other stipulations.

Though the first lady and the British royals weren’t likely obligated to wear the timeless, neutral shade for the banquet, white has long been a popular womenswear choice for formal, politically charged state visits, Marie Claire reports.

In 2011, then-first lady Michelle Obama also opted for an elegant white gown for a state dinner with the Queen.

In contrast, Ivanka, Tiffany and Lara Trump all went a bit bolder for the Monday night occasion – wearing pale blue, burgundy and black floral-printed frocks, respectively.

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Camilla, Duchess of Cornwall, right, meets First Lady Melania Trump after they arrived at Buckingham Palace. (Toby Melville/Pool Photo via AP)

Camilla, Duchess of Cornwall, right, meets First Lady Melania Trump after they arrived at Buckingham Palace. (Toby Melville/Pool Photo via AP)

White hues, however, ultimately ruled. Earlier in the day, FLOTUS and the Duchess of Cornwall both wore the summery shade through a busy agenda of events. The first lady’s ensemble quickly drew comparisons to similar styles previously sported by Princess Diana and Meghan Markle.

Ivanka Trump and Jared Kushner look on as U.S President Donald Trump places a wreath on the Grave of the Unknown Warrior during a tour of Westminster Abbey in central London. (Stefan Rousseau/Pool Photo via AP)

Ivanka Trump and Jared Kushner look on as U.S President Donald Trump places a wreath on the Grave of the Unknown Warrior during a tour of Westminster Abbey in central London. (Stefan Rousseau/Pool Photo via AP)

First daughter Ivanka, too, opted for a bright-white outfit and fascinator for a ceremonial welcome and tours the same day.

Fox News’ Andrew O’Reilly contributed to this report.