Anthony Albanese has attended a reception for leaders from across the world, hosted by King Charles III at Buckingham Palace, ahead of Queen Elizabeth II's funeral.
The prime minister met with Canadian prime minister Justin Trudeau on Sunday, before holding a lunch with Australia's community champions at Australia House in London.
Mr Albanese met with the new king along with his counterparts from the 14 Commonwealth realms.
The prime minister described the meeting as warm and friendly, saying it provided him a moment to personally offer his condolences to the King.
"It's a very personal bereavement that he's feeling," Mr Albanese told the BBC.
"In his case, of course, the loss of his mother coming so soon after the loss of his father.
"I was able to offer the condolences of the people of Australia for whom the Queen was held in great affection."
In Australia, senior Labor frontbencher Tanya Plibersek lauded the Queen's graciousness during her visits, with the environment minister having met the monarch briefly on two occasions.
"I have to say my mum came with me on both of those occasions," she said.
"She was super-excited; like a lot of women of her generation, she was a huge fan of the Queen and (she is) experiencing a lot of sadness at the moment."
Thursday will be marked by a day of mourning with Australians to get a one-off public holiday.
Idol star Anthony Callea will perform at the event, to be held at Parliament House in Canberra, with TV presenter Melissa Doyle to host.
"It will be an important day to pay tribute to the life and service of Queen Elizabeth II," Mr Albanese told Sky News.
All state and territory leaders, as well as justices of the High Court, will attend the service.
Mr Albanese said he and Opposition Leader Peter Dutton will give "short tributes" to the late monarch.
The prime minister also met with British prime minister Liz Truss in Kent on Saturday, where they spoke about national security in the Indo-Pacific.
Earlier in the day, Mr Albanese was forced to dismiss questions about changes to the constitution following the Queen's death, saying now was not the time.
"I don't think now's the time to discuss those issues, and I have made that clear," he said.
"This is a time in which we should acknowledge the life of service of Her Majesty Queen Elizabeth."
He said the late monarch had a "close affinity" to Australia, always standing with its people at "times of difficulty".
Mr Albanese said there was a standing invitation for King Charles to visit Australia, adding that he would be comfortable with the monarch continuing to express views on issues such as climate change.
"If he chose to do so, then of course that would be a matter for him. But I think that should be respected if he does choose to do so," he said.
The Queen's funeral will take place on Monday at 8pm AEST.
© AAP 2022