President Joe Biden and King Charles III met on Monday, but the royal family kept it casual.

The king didn't give Biden the "full Royal treatment" because it wasn't an official state visit, royal commentators and experts explained to Fox News Digital. Biden stopped by the United Kingdom for a quick meeting ahead of his appearance at the NATO summit.

The United States president was in the U.K. for less than 24 hours before heading to Lithuania.

Biden and King Charles' meeting was a "show of shared strength" between the two countries, according to Shannon Felton Spence, royal expert anddirector of global communications at Harvard’s Belfer Center.

PRINCESS KATE MIDDLETON, PRINCE WILLIAM, KING CHARLES SHOW OFF DAZZLING ROYAL ASCOT HATS

President Joe Biden photographed with King Charles

President Biden visited the U.K. to further strengthen the close relationship between the two nations and to discuss climate issues with King Charles III. (Chris Jackson/Getty Images)

"However, it’s not an official state visit, which is more formal and comes at the invitation of the head of state – which is the king," Spence explained. "The difference comes down to the protocol. It means that the king doesn’t provide the level of hospitality that he would on a state visit. The president is not the king’s guest on this trip. The president and the king are meeting today as two government officials and friends in order to discuss important matters. The king isn’t giving POTUS the full oryal treatment that he will on a state visit."

Because it was not an official state visit, Queen Camilla and Kate Middleton did not sport their famous tiaras.

"The palace was not given enough time to plan for a formal state visit, which can take up to a year to prepare, so the president’s visit is considered a ‘mini’ visit or working visit to differentiate," Kinsey Schofield, host of the "To Di For Daily" podcast, told Fox News Digital. 

"We will not see the Princess of Wales or the queen consort in tiaras due to the type of visit this is from the Biden administration," she added. "But what they lack in tiaras might be made up for in air fresheners as Queen Consort Camilla once famously complained about the president passing gas in front of her at COP26."

WATCH: BIDEN MEETS KING CHARLES FOR FIRST TIME SINCE SKIPPING CORONATION

Author of "The King," Christopher Andersen, noted that the seemingly casual meeting was "nothing out of the ordinary."

"Protocol dictates that the royal family pull out the stops for state dinners and formal banquets, not every time they're visited by a head of state – and that certainly includes the American president," he explained. "Even though this is a historic moment because it marks the first time President Biden has met King Charles since his ascension to the throne, the two men know each other and are comfortable in each other's company."

BIDEN MEETS KING CHARLES FOR FIRST TIME SINCE SKIPPING CORONATION

King Charles and Biden receive a royal salute

King Charles III receives President Biden at the dais in the Quadrangle before inspecting the Guard of Honour at Windsor Castle. (UK Press Pool/UK Press via Getty Images)

For Biden and the royal family, this won't be the first time they get together nor is the royal family "insulting" the president and first lady with the protocol of the "working" meeting.

"There is no question in my mind that King Charles and the rest of the royal family respect and admire the current occupants of the White House," Andersen added. "Any suggestion that the Windsors are in some way insulting the Bidens by not donning their full regalia is just silly, frankly. That day will come in the near future, when the president makes an official state visit and the king hosts one of those jaw-dropping state banquets his mother was so famous for."

Donald Trump and Queen Elizabeth II sitting

Donald Trump was the last U.S. president to visit the U.K. while Queen Elizabeth II was still alive. (Dominic Lipinski- WPA Pool/Getty Images)

Biden's trip to the U.K. marks the first time a U.S. president has visited the country since 2019, when Donald Trump came for a state visit that June. 

Joe Biden was given the "same special welcome" that previous presidents have enjoyed, according to British journalist and royal broadcaster Jonathan Sacerdoti. 

One thing different about Biden's visit was that "there wasn’t due to be a state banquet and no mention was made of the queen meeting him, nor the Princess of Wales."

Trump received the full royal welcome for his state dinner with Queen Elizabeth II. The monarch wore a white gown and accessorized with a crown as did Kate Middleton, now the Princess of Wales.

Trump and Queen Elizabeth II sharing tea

President Trump and Queen Elizabeth II make a toast during a state banquet at Buckingham Palace on June 3, 2019, in London. (Dominic Lipinski- WPA Pool/Getty Images)

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Biden arrived late Sunday evening and left shortly after meeting with the king and British Prime Minister Rishi Sunak briefly.

"We were told that Biden and the king discussed the climate, which is unusual as the content of the monarch’s discussions is not normally shared," Sacerdoti told Fox News Digital. "It’s actually quite ironic that Biden was said to be discussing climate change considering he arrived for this mini-trip on a massive jet (Air Force One) and was flown from one location to another in a fleet of helicopters, even being driven by car from the helicopter, which landed at Windsor Castle to meet the king only meters away."

Joe Biden and King Charles arrive inside Windsor Castle

King Charles III and President Biden arrive to meet participants of the Climate Finance Mobilisation forum at Windsor Castle on July 10, 2023. (Andrew Matthews - WPA Pool/Getty Images)

Many speculated about the relationship between the U.S. and U.K. when Biden declined to attend King Charles' coronation in May. However, presidents before him didn't attend any coronations either. First lady Jill Biden and the couple's granddaughter made an appearance instead.

"I’m not sure if tea and a photo with the king will have been enough to rebuild the image of unity between the two nations, but these things go through stronger and weaker moments all the time," according to Sacerdoti. "It is at least good that Biden stopped off to coordinate with the U.K. before the NATO summit, when there may be further disagreements between member states on matters including Ukraine, and also Swedish admission to the alliance."

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