(BBC) 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.