Canadian Prime Minister Justin Trudeau signed a book of condolence at Lancaster House in London on Saturday for Queen Elizabeth II.
He arrived in the British capital with other world leaders to attend the queen's funeral, which will be held on Monday.
International dignitaries arrived at Lancaster House throughout Saturday to sign the book.
Earlier, Prince William and his wife Kate joined King Charles and Queen Consort Camilla for a Buckingham Palace lunch with governors from the Commonwealth states.
The princess, who wore her hair down, was pictured smiling at the queen consort, who was holding a drink with a slice of lemon in it, as the pair chatted.
At one stage, Kate, who was wearing a long three-strand pearl necklace, placed her hand on the arm of Saint Lucia Governor-General Errol Charles as they spoke.
The princess also stood next to the king as he spoke to the dignitaries, while Prince William mingled in the busy room.
The governors of Antigua and Barbuda, Australia, the Bahamas, Belize, Canada, Grenada, New Zealand, Papua New Guinea, Saint Lucia, Saint Vincent and the Grenadines, the Solomon Islands and Tuvalu were among those present.
Earlier, the King and Prince William met members of the public.
Daniel Mendez, husband of the Governor-General of Belize Dame Froyla Tzalam, looked solemn as he wrote his thoughts in the book of condolence.
High Commissioner of Sierra Leone, Morie Komba, joined the officials as the book of condolence began filling up.
Prime Minister of Australia Anthony Albanese and his partner Jodie Haydon also attended Lancaster House.
Prime Minister of Antigua and Barbuda Gaston Browne has signed the book after arriving in the UK.
Governor-General of Belize Dame Froyla Tzalam looked moved as she wrote a tribute to the late queen.
Later on Saturday, President Joe Biden and his wife, Jill, were scheduled to travel to London for the funeral.
The Bidens, who joined the queen for tea in June 2021, are due to pay respects to the sovereign, whose coffin is lying in Westminster Hall, on Sunday.
Afterwards, they will sign an official condolence book before attending a reception hosted by King Charles.
