The King was greeted with military honours at Berlin's Brandenburg Gate earlier in the day as he began his visit to Germany, part of efforts to reset Britain's relations with Europe after its 2020 departure from the European Union.
"I have been struck by the warmth of the friendship between our nations," Charles said in a speech, delivered partly in German, at a state banquet in the German capital hosted by President Frank-Walter Steinmeier.
Highlighting the "generosity of spirit of the German people", the British monarch paid tribute to the nation's hospitality in hosting more than one million Ukrainian refugees.
In his ongoing focus on sustainability, Charles credited German expertise in organic farming as "greatly improving my own farms and soil".
Charles, who succeeded his mother Queen Elizabeth upon her death at 96 in September, had been due to travel first to France, but cancelled that part of the tour due to violent social unrest there.
The fact that Charles had picked European powers France and Germany for his first state visit, even before his coronation in May, was an important "European gesture", said Steinmeier, who greeted Charles and his wife Queen Consort Camilla in Berlin.
"Today, exactly six years after Britain started its exit from the European Union, we are opening a new chapter in our relations," Steinmeier said.
Over a three-day visit to Berlin, Brandenburg in the east and the northern port city of Hamburg, Charles will attend engagements reflecting issues facing both countries, such as environmental sustainability and the Ukraine crisis, and will also commemorate the past, according to Buckingham Palace.
As a mark of respect, fighter jets escorted Charles' plane into Berlin, where he became the first visiting head of state to be given a ceremonial welcome at the capital's most famous landmark, the Brandenburg Gate, a symbol of Germany's division during the Cold War and subsequent reunification.
Charles greeted hundreds of well-wishers lining the historic square and waving German and British flags, after listening to a rendition of the national anthem and watching as soldiers hoisted up the British flag on a mast.
Underscoring Charles' interest in environmental causes, one of his first engagements in Berlin was a forum on sustainability, addressing matters from hydrogen and renewables to industrial decarbonisation, according to Buckingham Palace.
There, he met German Foreign Minister Annalena Baerbock from the Greens party, junior partner in the country's three-way coalition, as well as business leaders, academics and civil society representatives.
"Today, we friends and partners, we are looking forwards - and that's why we are starting this state visit very consciously with a topic that is decisive for our future on this planet," said Steinmeier.
He said he was grateful that Charles had become involved in these issues early on. "We also benefit from your conviction today, your Majesty," said Steinmeier.
Charles will address the German lower house of parliament, the Bundestag, on Thursday in Berlin, and meet some of the Ukrainians who have taken refuge in Germany from Russia's invasion of their homeland.
"We are feeling just how deep our connection is especially in these times," Steinmeier said in his speech at the banquet. "Germany and the United Kingdom are today, also militarily, the two biggest supporters of Ukraine in Europe."
The German president gifted Charles a photo of his first visit to Germany as a young child in 1962 with his father, the late Prince Philip, to visit relatives. Charles has visited Germany on more than 40 occasions, as prince, including 28 previous official visits.
The British government makes the ultimate decision on such state visits, which form part of its use of the monarchy's "soft power".
As such, the trip was a clear sign of British Prime Minister Rishi Sunak's push to reset relations with Europe, said Anand Menon, director of academic think tank UK in a Changing Europe.
However, any warmer relations with Europe brought about by the visit could cool if other post-Brexit issues flare up.
Britain has slumped from Germany's fifth most important trading partner to 11th in 2022, behind the Czech Republic.