Vladimir Putin and the Prince of Wales remain on course for an awkward encounter next month - after the Russian president criticised the royal's reported comparison of him with Adolf Hitler.
In what he said was a message for the heir to the British throne, Mr Putin declared the criticism of his actions in Ukraine as "unacceptable" and "not what monarchs do".
His reaction highlighted the need for a serious round of diplomatic bridge building if the two men's attendance at a D-Day 70th anniversary event next month is not to prove an embarrassment.
The meeting between the two men is expected to take place in Normandy at "Sword Beach", the Second World War battle site where British troops stormed across the sand to attack Nazi positions.
Charles's reported remark came during a tour of the Museum of Immigration in Halifax, Nova Scotia, where he and the Duchess of Cornwall paid tribute to Second World War veterans and their families.
Jewish museum volunteer Marienne Ferguson, 78, told the Prince how she and her family fled the Nazis during the war, and said that he responded: "Putin is doing just about the same as Hitler" drawing an apparent parallel with Russia's annexation of the Ukrainian peninsula of Crimea in March.
Charles's remark has sparked particular anger in Russia because of the country's pride in its contribution to the defeat of Nazism in the Second World War, which cost the lives of an estimated 26 million Soviet citizens, including almost 8 million members of the military.
The Russian president was asked for his response by Press Association chief executive Clive Marshall during an interview with the world's leading news agencies in St Petersburg.
Mr Putin said: "It reminds me of a good proverb: 'You are angry. That means you are wrong.'"
In a direct personal message to the Prince, he added: "Give my words to Prince Charles. He has been to our country more than once, if he made such a comparison, it is unacceptable and I am sure he understands that as a man of manners."
Mr Putin added: "I met him personally, as well as other members of the Royal Family. This is not what monarchs do.
"But over the past few years we have seen so much, nothing surprises me any longer."
Mr Putin did not refer directly to Russia's wartime sacrifices in his response to the Prince's remark.
But he pointedly mentioned them earlier when discussing the upcoming anniversary commemorations at which he and the Prince are expected to join other world figures.
"During the Second World War, we were allies and we were fighting together against Nazism," said Mr Putin.
"As you know very well, the peoples of the Soviet Union and the people of Russia sacrificed a lot to win the war and achieve our joint victory over Nazism.
"That is why it is quite natural that we are going to have a meeting in Normandy and we are going to pay tribute to our coalition partners, to the British, the Americans and the French."
It is rare that someone's private opinion of an individual is known by that person, let alone a head of state of a foreign country. So there may well be some bridge building behind the scenes by aides on both sides if the men are to meet, and the meeting is to be cordial.
The process may already have begun as Charles is known to be a prolific letter writer. It is not the first time that his private views have become public and brought him criticism.
When the Prince's thoughts about Chinese officials became known - "appalling old waxworks" - following the handover of Hong Kong in 1997, it seemed likely that UK and Chinese relations would suffer long term.
But ties between the two countries have prospered and developed and the Prince has met a number of Chinese leaders in the intervening years.
During a 2007 visit to the United Arab Emirates, Charles criticised the fast-food chain McDonald's, telling a nutritionist he met at a diabetes centre in Abu Dhabi that banning the restaurants was "key".
The global company was said to have been disappointed by the comment but a few years later one of its senior executives attended an event hosted by one of the Prince's charities.
A spokeswoman for the Prince of Wales declined to comment on Mr Putin's criticism.