King Charles is "happy in his work", according to a royal expert

Royal biographer Robert Hardman told PEOPLE: "He is in good spirits. He is not having to second guess what Buckingham Palace might think on a particular issue, as he is in charge."

Charles also appreciated having the support of Camilla, 77, on the royal tour.

Robert said: "She keeps his spirits up and is a reassurance, but she also steps in here and there.

"We know she is not particularly keen on long-haul travel and yet has thrown herself into this trip."

The tour was Charles' first visit to Australia since he became the country's head of state in September 2022. The tour was also the monarch's biggest trip since his cancer diagnosis earlier this year.

In February, Buckingham Palace announced that Charles had been diagnosed with "a form of cancer".

The king underwent a "corrective procedure" for an enlarged prostate and doctors noticed a "separate issue of concern" that led to his cancer diagnosis.

The Palace said at the time: "During The King's recent hospital procedure for benign prostate enlargement, a separate issue of concern was noted.

"Subsequent diagnostic tests have identified a form of cancer.

"His Majesty has today commenced a schedule of regular treatments, during which time he has been advised by doctors to postpone public-facing duties.

"Throughout this period, His Majesty will continue to undertake State business and official paperwork as usual.

"The King is grateful to his medical team for their swift intervention, which was made possible thanks to his recent hospital procedure.

"He remains wholly positive about his treatment and looks forward to returning to full public duty as soon as possible."