The president and first lady landed on the grounds of Buckingham Palace by aircraft where they were greeted by Prince Charles and his wife Camilla. The couple received a royal gun salute as they walked to the palace, where Queen Elizabeth met them and took them inside.
While Trump is in the U.K. to strengthen ties between the two nations, his visit has already been clouded with controversy.
Here’s what you need to know about Trump’s visit.
WATCH: Queen Elizabeth pays tribute to U.S. soldiers, hopes shared interests continue
Not everyone is happy to see Trump
Before arriving in the U.K., Trump unleashed a Twitter tirade against London Mayor Sadiq Khan.
The move came after a newspaper column in which Khan said Trump did not deserve red-carpet treatment in Britain and was “one of the most egregious examples of a growing global threat” from the far right to liberal democracy.
″@SadiqKhan, who by all accounts has done a terrible job as Mayor of London, has been foolishly ‘nasty’ to the visiting President of the United States, by far the most important ally of the United Kingdom,” Trump tweeted before landing.
“He is a stone cold loser who should focus on crime in London, not me.”
Trump went on to say that Khan reminds him of “very dumb and incompetent” New York City Mayor Bill de Blasio, who has done a “terrible job” running the city.
Khan isn’t the only one unhappy with Trump.
Protesters are also demonstrating against the president’s visit, and anti-Trump banners have been hung in parts of the city.
WATCH: Activists protest Trump’s U.K. trip outside Buckingham Palace
At Buckingham Palace, activists were waiting with signs and chanting for Trump to “go home.” Posters had messages including “dump Trump” and “no to racism, no to Trump.”
Organizers say protests will continue into the evening on Monday and on Tuesday.
When Trump came to the U.K. in 2018, he was also met by demonstrators as thousands protested his visit across the city.
Trump tweeted on Monday afternoon that his visit so far “is going really well” and said the Royal Family has been “fantastic.” He denied seeing any protesters.
Trump won’t be seeing Meghan Markle
While he’s only been in the U.K. for a day, the president has already caused controversy around the Duchess of Sussex.
Trump called Meghan Markle “nasty” during an interview with British newspaper The Sun ahead of his meeting with the royals.
When asked if he was sorry to miss out on meeting American-born Markle and told that she “wasn’t so nice” about him during his campaign, Trump said: “I didn’t know that. No, I hope she’s OK. I did not know that.” (The Duchess of Sussex is not meeting Trump as she is on maternity leave from royal duties.)
When told that Markle once said she might move to Canada in 2016 if Trump was elected, he responded that he “didn’t know that she was nasty.”
Markle supported Hillary Clinton, the Democratic presidential candidate in 2016, and called Trump “divisive” and “misogynistic” at the time.
Trump said later that he thought Markle would be “very good” as a royal and claimed he only meant her comments were “nasty.”
WATCH: Trump says UK showed world ‘what it means to be British’ in Second World War
Trump will have a “lavish” dinner with the royals
On Monday evening, Trump and Melania will have dinner at Buckingham Palace with members of the Royal Family, including the Queen.
CNN reports that 170 guests are expected, including Trump’s children Ivanka Trump, Donald Trump Jr., Eric Trump and Tiffany Trump.
Demonstrators are expected to protest outside, including the possible return of an inflatable balloon depicting the president as a baby.
Vox reports that protesters “have upped the ante” for this state visit and are reportedly planning to unveil a 16-foot robot of Trump texting while sitting on a golden toilet. The toilet apparently “farts” and says: “No collusion.”
Trump will meet with Theresa May
On Tuesday, Trump and British Prime Minister Theresa May will host a business breakfast attended by the Duke of York at St James’ Palace.
The BBC reports that Trump will then visit Downing Street to talk with May, followed by a joint press conference. May is stepping down as prime minister on June 7 after failing to secure to Brexit deal.
It is unclear how Trump will interact with May as, a year ago, he blasted the British prime minister in an interview hours before she hosted him for dinner. Though he has spared May so far this time, he has praised her rival, prime ministerial hopeful Boris Johnson.
Trump will finish his visit in Ireland
On Wednesday morning, the president is expected to travel to Portsmouth alongside the Queen and Prince Charles for a D-Day commemoration.
After that event, Trump will make his first presidential visit to Ireland. He will spend two nights at his golf club in Doonbeg, which sits above the Atlantic.
After Dublin balked at holding a meeting there, a deal was struck for Trump to meet Irish Taoiseach Leo Varadkar at Shannon Airport.
—With files from the Associated Press