Donald Trump and First Lady Melania Trump welcomed the royals to the White House on Monday evening, where they are scheduled to meet separately over a cup of tea.
The four-day visit is proceeding as planned, despite this weekend's attack on a gala dinner in Washington, DC, which raised questions about security ahead of the king's arrival.
Donald Trump, who was unharmed in the shooting, has said he is looking forward to the visit. In an interview with Fox News, he called King Charles “brave” and a “fantastic person” who has been a longtime friend.
The state visit could also be a tricky diplomatic balancing act for the British monarch, at a time of increasing transatlantic tensions.
Trump has criticized Britain's refusal to participate in a war with Iran and threatened to tear up the trade agreement between the countries. The Trump administration has also considered reassessing Britain's rights to the Falkland Islands, according to media reports.
Trump has insisted that the political rift should not affect the visit - but he has nevertheless said before the visit that the king can "absolutely" help repair the relationship between the countries.
"Absolutely. He's fantastic. He's a fantastic man. The answer is absolutely yes," Trump said in response to such a question from the BBC.
The last British state visit to the United States was in 2007, when the late Queen Elizabeth II was received by then-President George W. Bush.
