Justin Trudeau's office has defended the Canadian PM, after he was filmed singing by a piano in a London hotel, two days before the Queen's funeral.
In a video shared on social media, the prime minister can be seen singing Bohemian Rhapsody by the British rock band, Queen.
The Queen was Canada's head of state, and Mr Trudeau designated 19 September a national day of mourning in Canada.
Critics accused the PM of a lack of respect - but others defended him.
The video has been shared on social media, but while a spokesperson for the prime minister confirmed it was genuine, it is not clear who filmed it.
It was taken at the Corinthia, where the Canadian delegation was staying, on the evening of Saturday 17 September.
Mr Trudeau can be seen in a T-shirt, leaning on a piano as Gregory Charles, a musician from Quebec and recipient of the Order of Canada, plays Bohemian Rhapsody.
He sings famous lyrics including "easy come, easy go, little high, little low", and "any way the wind blows".
Mr Charles told Canadian newspaper the Globe and Mail the group sang with him for two hours, and that it was "a lot of fun", reminding him of Caribbean funerals in blending sombre moments with those celebrating life.
But the video has drawn criticism from some Canadian commentators and members of the public.
"Embarrassing doesn't even begin to cover it," wrote Andrew Coyne, Globe and Mail columnist, on Twitter.
"He's the prime minister, in a public place, on the eve of the Queen's funeral. And this is how he behaves?"
Vivian Bercovici, a former Canadian ambassador to Israel, said: "He is the Canadian prime minister representing Canada at a week of mourning for the Queen. Our head of state. This isn't about Justin. But he should grow up."
But others said the issue had been exaggerated.
Emmett Macfarlane, an associate professor of political science at the University of Waterloo, Ontario, wrote on Twitter: "He's... singing. Of all the embarrassing things Justin Trudeau has said and done, this doesn't rank."
A spokesperson for Mr Trudeau said: "After dinner on Saturday, [the] prime minister joined a small gathering with members of the Canadian delegation, who have come together to pay tribute to the life and service of Her Majesty.
"Gregory Charles, a renowned musician from Quebec and Order of Canada recipient, played piano in the hotel lobby which resulted in some members of the delegation including the prime minister joining."
The spokesperson pointed out "the prime minister has taken part in various activities to pay his respects for the Queen".
Some took a light-hearted view of the issue.
Music journalist Adam Feibel joked: "I don't think that Justin Trudeau singing Bohemian Rhapsody was disrespectful to the queen but I know enough about karaoke to assume it was disrespectful to Queen."