French President Emmanuel Macron said the United Kingdom and France will "save Europe" as he was hosted by King Charles III at a lavish state banquet at Windsor Castle.
The king spoke of his confidence in ties between the countries as the pair dined alongside members of the royal family and celebrity guests.
The three day visit is the first by a French president since 2008, and the first by a European Union political leader since Brexit.
Addressing both Houses of Parliament, Mr Macron said the two countries needed to come together to strengthen Europe, including on defence, immigration, climate and trade.
"The United Kingdom and France must once again show the world that our alliance can make all the difference," he said.
"The only way to overcome the challenges we have, the challenges of our times, will be to go together hand in hand, shoulder to shoulder."
The French president also called for the UK, France and Europe to strengthen security by investing in technology and reduce "excessive dependencies on the US and China".
Other senior royals were among the 160 guests, including Catherine, Princess of Wales.
The princess has been absent from the last few ceremonial state dinners, with the South Korean state visit in November 2023 the last she attended.
There were also an abundance of celebrity guests, including Elton John and The Rolling Stones frontman Mick Jagger.
A royal welcome
Earlier in the day, the French president and his wife, Brigitte Macron, were treated to the full force of British ceremonial charm.
The Macrons were greeted at London's RAF Northolt air base by Prince William and Princess Kate before being met by the king and Queen Camilla in Windsor.
They were driven to the almost 1,000-year-old royal residence of Windsor Castle in horse-drawn carriages, through streets bedecked in Union Jacks and French tricolour flags.
During his state banquet speech, Charles spoke of the deep cultural, political and historical ties between the two nations.
He also spoke of efforts to tackle "irregular migration across the English Channel", "complex threats" and providing support for Ukraine.
"As friends and as allies, we face them together," Charles said.
The 76-year-old, who is undergoing treatment for cancer, had a noticeably red eye.
A Buckingham Palace source said he suffered a burst blood vessel that was unrelated to any other health condition.
New tactics to stop boats
Politics will take centre stage on Wednesday, when Mr Macron sits down for talks with UK Prime Minister Keir Starmer on migration, defence and investment.
Mr Starmer and Mr Macron are expected to discuss ways to stop migrants from crossing the English Channel in small boats, and try to advance plans for a post-ceasefire security force for Ukraine.
Thousands of migrants each year use northern France as a launching point to reach the UK, either by stowing away in trucks or in small boats across one of the world's busiest shipping lanes.
The UK has struck a series of deals with France over the years to increase patrols of beaches and share intelligence in an attempt to disrupt the smuggling gangs.
It has only had a limited impact.
About 37,000 people were detected crossing the English Channel in small boats in 2024, and more than 20,000 people made the crossing in the first six months of 2025.
British officials have been pushing for French police to intervene more forcefully to stop the boats, and welcomed the sight of officers slashing rubber dinghies with knives in recent days.
France is also considering a UK proposal for a "one-in, one-out" deal that would see France take back some migrants who reached Britain, in return for the UK accepting some of those in France.
Macron said the leaders would try "to fix today what is a burden for our two countries".
"France and the UK have a shared responsibility to address irregular migration with humanity, solidarity and fairness," he said.
Princess spotted with tiara for first time since 2023
At the state banquet, Kate wore the Lover's Knot Tiara, a pearl and diamond diadem which was originally created for Queen Mary in 1914.
It was also previously worn by Queen Elizabeth II, who gifted it to Princess Diana after she married into the royal family in 1981.
Following the divorce of Charles and Diana, the tiara was returned to the queen.
Kate brought the famed tiara out of retirement at a diplomatic reception in 2015 — it had remained previously unworn since Diana last donned it at an event in Brazil in 1991.
The Princess of Wales's last tiara appearance was in 2023.
The reason for the hiatus is partially due to her stepping out of the spotlight for most of 2024 while she focused on cancer treatment.
Last week, she spoke about her "rollercoaster" cancer recovery at a hospital in eastern England.
ABC/wires
