The King, 75, remains hopeful that he will be able to make the trip to Australia, which is hosting the annual Commonwealth Heads of Government meeting (CHOGM).
Palace aides are looking at the proposed schedule and will begin making tentative plans in the coming weeks, with site visits said to be in the pipeline.
However, sources cautioned that it was still early days and that such future trips were wholly reliant on how the King reacts to ongoing treatment in the coming months.
“It is no great mystery that the King is keen to attend CHOGM if he is able,” one said.
His appearance at the traditional Easter Matins service at St George’s Chapel, Windsor, was considered a “significant first step” amid “great hope and optimism” from his medical team.
The monarch smiled broadly as he greeted members of the public after the service, shaking hands as he thanked them for their good wishes with a promise that he was “doing his best”.
The King was diagnosed with an undisclosed form of cancer in January, after undergoing treatment for an enlarged prostate.
He immediately began a course of weekly treatment which proved so successful that his doctors adjusted their guidance on the level of public duties he is now able to undertake.
As such, the King is hoping to attend Trooping the Colour, his official birthday celebration, on June 15, as well as the 80th anniversary commemorations of D-Day the previous week.
However, sources note that treatment continues and that “caution remains the watchword”.
An invitation has been extended for him to attend the Melbourne Cup on November 5, an event he first attended with Diana, Princess of Wales in 1985 before returning with Camilla, then Duchess of Cornwall, in 2012.
The King has also been invited to The Everest race day in Sydney on October 19, when organisers hope he will be able to present the trophy for a race named in his honour, the King Charles III Stakes.
A visit is also expected to include attendance at the bicentenary celebrations of the New South Wales parliament’s upper house.
Local tourism chiefs have also mooted trips to Taronga Western Plains Zoo in Dubbo, the Queen Victoria Building in the heart of Sydney and its iconic Opera House.
However, plans are likely to be scaled back with the tour closer to two weeks rather than three. A trip to Fiji is said to have been ruled out.
The King’s schedule, which typically involves six or seven engagements a day, would also be reduced to include “significant downtime”.