Paris , France:
Our relations have of course not always been entirely straightforward," Charles said.
King Charles III on Thursday follows in his mother Queen Elizabeth II's footsteps by addressing lawmakers in the French upper chamber of parliament on the second day of a visit that has seen him urge stronger ties between the countries.
At a lavish state banquet late Wednesday, Charles issued a call for France and the UK to reinvigorate their relations, in comments echoed by French President Emmanuel Macron.
It is "incumbent upon us all to reinvigorate our friendship to ensure it is fit for the challenge of this, the 21st century," Charles said in a toast.
Macron added that "despite Brexit... I know, your majesty, that we will continue to write part of the future of our continent together, to meet the challenges and to serve the causes we have in common".
"Our relations have of course not always been entirely straightforward," Charles said, in a speech in both English and accented but clearly-spoken French that impressed his hosts.
But he set out an optimistic vision of the Entente Cordiale, the pact between the two neighbours forged in 1904, calling it a "sustainable alliance".
Charles' speech at the Senate, France's upper house of parliament, is the diplomatic high point of a more informal day. The late queen addressed the Senate in 2004 but not in the chamber itself.
He will then visit the northern Parisian suburb of Saint-Denis -- home to the French national stadium used for the Rugby World Cup, and the Olympics next year -- where he is expected to see residents and sports stars.
Also heading to the Ile de la Cite on the river Seine, Charles -- a keen gardener who once admitted he talked to his plants -- will tour a flower market named after Queen Elizabeth II on her last state visit in 2014.
From there, he will view renovation and reconstruction work at the nearby Notre-Dame Cathedral, which was partially destroyed by a devastating fire in 2019.
Nearly 1,000 people are working to restore the cathedral, that dates back to the 12th century and is considered one of the finest examples of French Gothic architecture.
Following the fire, Charles said in an emotional message to Macron that he was "utterly heartbroken", calling Notre-Dame "one of the greatest architectural achievements of Western civilisation".
The Paris leg of the state visit wraps up with a formal farewell from Macron at the Elysee Palace.
The visit, which was rescheduled from March due to mass protests against French pension reforms, also aims to showcase Charles's stature as a statesman just over a year after the death of Queen Elizabeth II.
The original itinerary in Paris and the southwestern city of Bordeaux is largely unchanged, and is packed with ceremony and pomp in a country that abolished its monarchy in the 1789 revolution and executed its king.
On Wednesday, Macron and Charles were seen chatting amicably while driving down the Champs-Elysees for talks at the Elysee Palace.
After their talks, the pair walked the short distance to the residence of the British ambassador, pausing to shake hands with well-wishers on the upscale Rue du Faubourg Saint-Honore.
The French president is known to have a strong personal rapport with Charles, with both men known for their love of books.
Macron presented Charles with a book by the 20th-century French writer Romain Gary, while he received a special edition of Voltaire's "Lettres sur les Anglais" ("Letters on the English").
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