"As you know, the King has a deep and broad relationship with Australia, and his Majesty's warmth for our country was evident in our brief conversation this afternoon," Lynette Wood told reporters in London on Monday morning Australian time.
"Having visited Australia 16 times, including studying in Victoria, His Majesty knows Australia very well."
The diplomat, who was the first Australian official to formally meet the new King, also remarked on the mood in London following the death of Queen Elizabeth II, aged 96, late last week.
"What is really striking me in these past few days is the solemnity here in London, and the regard with which her Majesty is held and the strong support that is already there for King Charles III," she said.
Later this week, the acting commissioner will greet Prime Minister Anthony Albanese and Governor-General David Hurley when they arrive in London ahead of the Queen's funeral on September 19 at Westminster Abbey.
Both men will depart Australia on Thursday.
Mr Hurley on Sunday proclaimed the new king's accession in a ceremony at Parliament House in Canberra.
After Mr Hurley read out the proclamation, God Save the King was played and a 21-gun salute rang out across the nation's capital.
Flags were also raised to full mast to honour the King, before being lowered again on Sunday evening. Flags will remain at half mast until the day after the funeral.
"Australia is an unfinished product. It is now entering a new era," Mr Hurley told reporters on Sunday.
"Most Australians have not known a world without Queen Elizabeth II. Her passing is the end of an era."
A national memorial service for the Queen will be held in Canberra on September 22 as the country observes a one-off public holiday for a national day of mourning.
"I encourage all Australians, wherever you may be, to take time to pause and reflect on Her Majesty's extraordinary life of service," Mr Albanese said on Sunday.
Elsewhere, Victoria will on Monday proclaim the King as Australia's new head of state.
Victoria's Lieutenant-Governor, Chief Justice and other senior officers will swear oaths to the King in a proclamation ceremony at Government House.
All states except Victoria held their own proclamation ceremonies on Sunday.
Federal parliament has been suspended this week but some state parliaments will sit briefly on Tuesday to hear condolence motions.
In Victoria, MPs will also be required to swear allegiance to King Charles III.
Overnight in the UK, the Queen's coffin was driven from Balmoral Castle, where she died, to Scotland's capital, Edinburgh.
Her body will be flown to London on Tuesday where it will remain at Buckingham Palace before being taken to Westminster Hall to lie in state for four days.
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