King Charles has hailed the AUKUS defence pact during US President Donald Trump's unprecedented second state visit to the United Kingdom.
The king is hosting Mr Trump at a state banquet at Windsor Castle, which is also being attended by high-ranking US officials and tech CEOs.
In his speech to the banquet, King Charles said the alliance between the UK and US was the "closest defence, security and intelligence relationship ever known" and he also stressed the importance of the trilateral AUKUS pact, which includes Australia.
"Today, as tyranny once again threatens Europe, we and our allies stand together in support of Ukraine to deter aggression and secure peace," he said.
"And our AUKUS submarine partnership, with Australia, sets the benchmark for innovative and vital collaboration."
AUKUS, which was signed by Mr Trump's predecessor Joe Biden, has been surrounded by uncertainty since the current president's election late last year.
Earlier, Mr Trump and his wife, Melania, were greeted by Prince William and Catherine, Princess of Wales, in the Walled Garden of Windsor Castle as he stepped off his presidential helicopter, Marine One.
He met King Charles III and Queen Camilla on the castle's east lawn as a 41-gun salute was fired, while a similar display occurred at the Tower of London, in the centre of the capital.
Some 120 horses and 1,300 members of the British military took part in the ceremony, which UK officials say marked the largest military ceremonial welcome for a state visit to Britain in living memory.
The Trumps and the royals then embarked on a carriage procession through the Windsor estate towards the nearly 1,000-year-old castle.
The pair sat in the same carriage during the short journey to the castle's quadrangle, where they inspected a guard of honour.
Britain is going the extra mile to dazzle and flatter the unpredictable US president with an extraordinary show of pomp and pageantry as it tries to keep him onside during a host of international crises.
The military welcome was even bigger than when Queen Elizabeth II hosted Mr Trump on his previous state visit in 2019.
Bad weather stopped the first joint fly-past by US and UK F-35 military jets, but a scaled-back Royal Air Force Red Arrows display went ahead.
The Trumps also laid a wreath on the tomb of Queen Elizabeth II, who died in 2022.
While the US president visited Windsor, protesters hit the streets of London and outside the estate, angry about his visit.
Some 1,600 officers were deployed to deal with a demonstration by the "Stop the Trump Coalition" in London alone.
"Trump doesn't want to see any opposition. And you know, that's just what he's about, isn't it," said Lynn Iliffe, a pensioner from Stratford in east London.
She was brandishing a poster spelling out an acronym of Trump's name as "Tyrant, Racist, Untruthful, Misogynist, Putinist".
Others were more circumspect.
"It would have been nice for us to see the president," said Charlene Bryan, who had made a special trip from London to revel in the events.
"You know, some of them want to welcome the president, so it's quite sad that the public cannot see the president."
Ahead of his visit, London Mayor Sadiq Khan, who has a long-running feud with the US president, wrote in The Guardian that Mr Trump had "perhaps done the most to fan the flames of divisive, far-right politics around the world in recent years."
Mr Trump will not visit the UK's capital during this trip and did not visit during his first, in 2019.
The pair have traded barbs since Mr Khan became London's mayor in 2016.
State visit designed to flatter Trump
The state visit was all designed to appeal to a US leader who this year crowed "LONG LIVE THE KING!" about himself on social media before the White House posted a fake magazine cover of him wearing a crown.
British Prime Minister Keir Starmer will be hoping Mr Trump leaves on Thursday feeling the warm glow of royal soft power — but there are no guarantees.
Mr Trump appeared to be feeling the love as he arrived by helicopter at the US ambassador's official residence in London on Tuesday with First Lady Melania Trump.
"A lot of things here warm my heart," said the president, whose mother hailed from Scotland and who owns two golf resorts in the country.
He described the king, 76, who is undergoing treatment for cancer, as "my friend".
The Republican may also relish a chance to escape a turbulent period at home in the United States, where the killing of right-wing activist Charlie Kirk has caused deep turmoil.
But the spectre loomed of late sex offender Jeffrey Epstein, who has provided domestic headaches for both Mr Trump and Sir Keir Starmer and who has caused the royal family considerable embarrassment.
Police arrested four people after they projected images of Mr Trump and Epstein onto Windsor Castle late on Tuesday.
Mr Starmer will host Mr Trump on the second day of the visit on Thursday at his country residence, Chequers, where a host of issues, including the UK's recent trade deal with the US, is set to be discussed.
The pair will be buoyed by British pharmaceutical group GSK's announcement that it will invest $30 billion in the United States over the next five years but talks could turn awkward on several fronts.
The UK prime minister in particular faces political troubles at home, after sacking his UK ambassador to Washington, Peter Mandelson, over a furore involving the diplomat's connection to the late Epstein.
ABC/wires
