Russia dismisses such comparisons and says Russian-speakers in eastern Ukraine are under threat from a Kiev government in the sway of militant Ukrainian nationalists.
The Daily Mail said the prince's comments were made during a conversation with Marienne Ferguson, 78, who lost relatives during the Holocaust, when they spoke at a Museum in Halifax, Nova Scotia, where she works as a volunteer.
"I had finished showing him the exhibit and talked with him about my own family background and how I came to Canada," she told the paper.
"HEARTFELT"
"The prince then said 'And now Putin is doing just about the same as Hitler. I was very surprised that he made the comment as I know they (Britain's royals) aren't meant to say these things but it was very heartfelt and honest."
A spokeswoman for Charles's office said they did not comment on his private conversations.
"We would like to stress that the Prince of Wales would not seek to make a public political statement during a private conversation," she said.
Traditionally, Britain's royal family does not voice political views in public with the head of state merely a constitutional figurehead. During her long reign, Queen Elizabeth has never aired any such personal sentiments.
However, Charles has often courted controversy by voicing strong views on the environment, architecture and social affairs. Last year it was revealed he had held 36 meetings with government ministers since Prime Minister David Cameron's Conservative-led coalition took power in 2010.