King Charles and Queen Camilla will head to Australia and Samoa next month in what has been described as a major test of the King’s stamina amid his ongoing cancer treatment.

King Charles will head to Australia next month (Image: Getty)

Queen Camilla’s son has given a brief health update on King Charles as he travels the country promoting his new cookery book, Cooking and The Crown.

Tom Parker-Bowles, a food critic and writer said His Majesty’s “treatment is going well” and spoke about how his mother was coping with the diagnosis.

The King was diagnosed with an undisclosed form of cancer at the start of the year and has been undergoing outpatient treatment ever since.

Discussing this, Mr Parker Bowles said his “doctor says the treatment is going well” and shared that Camilla was coping well, adding: “She’s tough, my mother”.

It comes as the couple prepare to travel to Australia and Samoa next month. The long trip, spanning 12 time zones, is a sign the 75-year-old monarch is recovering well, with a source stating his health is “heading in a positive trajectory”.

The visit will be the King’s biggest overseas trip since he began treatment for cancer in February.

Charles and Camilla will arrive in Australia on October 18 and will spend six days in the country before flying to Samoa for the Commonwealth Heads of Government Meeting (CHOGM). They will return to the UK on October 26.

The schedule Down Under encompasses just three days of engagements to allow sufficient time for the King to rest.

A Buckingham Palace spokesman said: “We’ve had to, as you would with any visit, think about how you can ensure Their Majesties energies are preserved to be at their best.”

He added: “There had been some hope earlier in the year for Their Majesties to be able to visit New Zealand and on doctors’ advice that unfortunately wasn’t able to take place. We’ve had to make some tough decisions with the Australian Government where [Their Majesties] can get to.”