Brexit Party leader Nigel Farage has criticised members of the Royal Family and claimed the Duke of Sussex's popularity has "fallen off a cliff" since he met his wife, Meghan.
Mr Farage also said he hoped Prince Charles would not become king because of his views on climate change.
But the ex-UKIP leader told the right-wing conference in Australia the Queen was an "amazing, awe-inspiring woman".
His spokesman said the comments were not part of a speech at the event.
The comments were first reported by the Guardian, which said media had been banned from the Conservative Political Action Conference in Sydney but that it had heard a recording of Mr Farage comments on Saturday.
It reported Mr Farage had said Prince Harry had been "the most popular royal of a younger generation that we've seen for 100 years" before he met Meghan.
"Here was Harry, here he was this young, brave, boisterous, all-male, getting into trouble, turning up at stag parties inappropriately dressed, drinking too much and causing all sorts of mayhem," he said.
"And then he met Meghan Markle, and it's fallen off a cliff."
He went on to discuss the prince's remarks last month that he and Meghan plan to have no more than two children to help fight against climate change.
Mr Farage said the move was "irrelevant" because the "population of the globe is exploding" in areas including China and India.
He said he hoped the Queen would live a "very, very long time" to prevent the Prince of Wales becoming king.
"When it comes to her son, when it comes to Charlie Boy and climate change, oh dear, oh dear, oh dear," he said.
"Her mother, Her Royal Highness the Queen's mother was a slightly overweight, chain-smoking gin drinker who lived to 101 years old.
"All I can say is Charlie Boy is now in his 70s... may the Queen live a very, very long time."
Mr Farage's comments have been criticised on social media, with Labour MP David Lammy urging Mr Farage to "lay off Meghan".
And BBC political correspondent Mark Lobel said Number 10 was refusing to give the remarks any more oxygen by commenting on them.
But one Brexit Party MEP dismissed the criticism saying Mr Farage's comments were "wholly irrelevant to our goal of delivering Brexit".
Another MEP said: "Sounds like he was having fun with the Australians. He said the Queen was an amazing woman.