Prince Charles is reported to have compared the actions of Russian leader Vladimir Putin to Nazi dictator Adolf Hitler.
The Prince of Wales appeared to back growing international anger from the West at Russia's actions in Ukraine during his tour of Canada when he spoke to a woman who fled the Nazis and lost family members during the Holocaust.
His remark came during a tour of the Museum of Immigration in Halifax, Nova Scotia, when the Prince and the Duchess of Cornwall paid tribute to Second World War veterans and their families.
Jewish museum volunteer Marienne Ferguson told the Prince that she fled to Canada with her family shortly before the Nazis annexed the Baltic coastal Free City of Gdansk in 1939.
After meeting Charles, Mrs Ferguson, 78, said: "The Prince said, 'And now Putin is doing just about the same as Hitler'.
"I must say that I agree with him and am sure a lot of people do.
"But I was very surprised that he made the comment as I know they (members of the Royal Family) aren't meant to say these things.
"I told the Prince that while my family and I were lucky to get a permit to travel, many members of my relatives had permits but were unable to get out before the war broke out on September 1.
"They were sent to the concentration camps and died."
A spokesman for Clarence House said: "We do not comment on private conversations. But we would like to stress that the Prince of Wales would not seek to make a public political statement during a private conversation."
Charles is due to meet Mr Putin in a few weeks when he attends the 70th anniversary of the D-Day landings in Normandy on June 6.
He and the Duchess are currently on a four-day tour of Canada.