The couple are in the United Kingdom for the late monarch's funeral, which takes place at Westminster Abbey on September 19.
WATCH: The Queen's eight grandchildren stand vigil at her coffin
They were seen queuing inside the oldest building on the U.K. parliamentary estate along with Ralph Goodale, the Canadian High Commissioner to the United Kingdom, and bowing as they passed in front of Her Majesty's coffin.
Justin and Sophie paid their respects to Queen Elizabeth II on Saturday
Justin and Sophie also signed a book of condolence for the Royal Family at Lancaster House, after which the prime minister had his first audience with King Charles III at Buckingham Palace. He also visited 10 Downing Street for a meeting with U.K. Prime Minister Liz Truss.
Justin and Sophie both left a message in the book
Justin has known the King for many years, since his father, late former Canadian Prime Minister Pierre Trudeau, introduced him to the late Queen when he was a boy. As prime minister, Justin has also welcomed the King and Queen Consort to Canada on many occasions.
The King and Canada's prime minister had a good meeting, despite the sad circumstances
The King and Justin last saw each other in May, when Charles and Camilla – now the Queen Consort – visited Canada on a three-day tour of Newfoundland, Ottawa and the Northwest Territories as part of the celebrations for the late Queen's Platinum Jubilee.
U.S. President Joe Biden and First Lady Dr. Jill Biden also visited the Queen's coffin at Westminster Hall to pay their respects, doing so on September 18. They will also attend the funeral.