Queen Elizabeth II welcomed US President Donald Trump to Buckingham Palace, her main residence in central London, as he began a three-day state visit to Britain on Monday.

Prince Charles, the queen’s eldest son and heir to the throne, and his wife Camilla, the duchess of Cornwall, greeted Trump and his wife Melania as they landed by helicopter on a palace lawn.

Trump and Charles inspected a guard of honour, chatting to several soldiers before returning inside the palace for a private lunch ahead of an evening banquet.

Trump’s daughter Ivanka and son-in-law Jared Kushner also watched the welcoming ceremony from a palace balcony.

Thousands of protesters, led by women’s groups, plan to hold a rival “people’s banquet” in nearby Parliament Square while Trump enjoys the royal banquet at Buckingham Palace.

A larger anti-Trump march through central London is scheduled on Tuesday, when the US president will meet British Prime Minister Theresa May and US and British business leaders.

Trump’s arrival in London was overshadowed by his tweets insulting Sadiq Khan, London’s first Muslim mayor.

Trump, who has had previous Twitter feuds with Khan, called him “a stone cold loser who should focus on crime in London, not me.”

Khan had given several interviews to British media ahead of the visit, writing in Sunday’s Observer newspaper that it was “un-British to roll out the red carpet” to Trump.

The visit, planned to commemorate the 75th anniversary of the D-Day landings, comes as Britain remains in the throes of the Brexit process and as May plans to step down on Friday as leader of her Conservative party.

Trump has endorsed the favourite to succeed May, pro-Brexit former foreign secretary Boris Johnson, as an “excellent” candidate.

“I have always liked him. I don’t know that he is going to be chosen, but I think he is a very good guy, a very talented person,” he told Friday’s edition of The Sun, one of Britain’s most popular tabloid newspapers.

Trump also commented on Brexit ahead of his visit, telling The Sunday Times it was a mistake not to involve anti-EU campaigner Nigel Farage in the negotiations on Britain leaving the bloc.

He said Farage, who leads a new Brexit Party, was a “very smart person” with much to offer.

“They won’t bring him in,” Trump told the newspaper. “Think how well they would do if they did.”

Farage praised Trump on Monday, saying he “comes offering a trade deal if we need one, but also American’s hand of friendship.”

“As the democratically elected leader of the free world, we should extend to him a welcome that befits the status of his office and great country,” Farage tweeted.

Trump’s visit to Britain will be capped on Wednesday with a large ceremony in the southern city of Portsmouth to mark the the D-Day landings in 1944, when some 160,000 British, US, French and other Allied troops landed in Normandy, in German-occupied western France, in World War II.

The president will then travel to Ireland and France.