'You've only got this window to do it': Why King Charles' visit to Australia had to happen now

EXCLUSIVE: When King Charles III announced to the world, via Buckingham Palace, that he had been diagnosed with cancer, it immediately put into doubts the monarch's plans for the year ahead.

It was February 5 and the King was into his second year of his reign following the death of his mother, the late Queen Elizabeth II.

The transition from mother to son had so far been seamless, but the King's cancer diagnosis threatened to overshadow what had so far been a successful and smooth run as sovereign.

READ MORE: Looking back at King Charles' previous visits to Australia

The announcement came weeks after the King's planned surgery on an an enlarged prostate at The London Clinic, the same hospital where the Princess of Wales was recovering from abdominal surgery.

The discovery of the King's cancer came during his surgery at the facility, but the palace declined to reveal the type of cancer Charles III had been diagnosed with.

READ MORE: Where you can see the King and Queen in Australia

On doctors' orders, the King immediately started a schedule of regular treatments and postponed his public-facing duties.

It was unclear, to the public at least, how long the King would be out of action for and the impact it would have on his future engagements including a rumoured visit to Australia in the months ahead.

"If you asked me earlier this year I would have said, 'I don't think this visit is going to happen – he's got cancer, how can he travel to the other side of the world?'" ITV's royal editor Chris Ship tells 9honey.

Watch the video above.

"There's no doubt it's been a really, really challenging year for the royal family, for the King, personally, with his health issues, for his family with his daughter-in-law Kate having her cancer treatment so this visit is really important."

The King and Queen Camilla arrive in Sydney tonight night for a five-day tour, but engagements are scheduled across just three days.

"Because of his health difficulties, he's having to shorten the visit," Ship explains.

"He's having to forego evening events...there's a lot of changes that have happened.

READ MORE: 'Tough and gruelling': Royal reporter's experience with Harry and Meghan

"But at least he is able to make it to Australia as the King of Australia and of course, this is the first time he's been here as monarch."

The King has a planned rest day on Saturday to allow the 75-year-old to recover from the long flight. Official engagements begin in Sydney on Sunday, before moving to Canberra on Monday and again in Sydney on Tuesday.

The King and Queen depart for Samoa on Wednesday morning.

Ship, who has travelled to Australia as part of the British press pack covering the visit, says the tour was able to happen now because it coincided with the Commonwealth Heads of Government Meeting (CHoGM) in Samoa.

"That gave the King's doctors a very limited time to deal with," Ship says.

"If you're going to do Australia and travel there, if you're going to go to Samoa and go to the first Commonwealth meeting as head of the Commonwealth as he is now, then you've only got this window to do it."

His Majesty's doctors have given permission for the monarch to temporarily stop his weekly treatment for cancer during the journey, which spans 11 days including nine of engagements and two for travel on either side.

READ MORE: Queen Camilla to visit Aussie charity she is patron of

The King will travel with two doctors who will carry a supply of the monarch's blood, to ensure an exact match if a transfusion was needed. Similar arrangements were in place when the late Queen used to travel abroad.

Charles will be visiting Australia for the 17th time, but it is his first tour as monarch which, in itself, is a history-making endeavour. It is also the first time a British King has been here.

"If you're going to be the Head of State of 14 realms outside the United Kingdom, you need to go see them," Ship says.

"And of course, the last time the monarch was here was the late Queen Elizabeth in 2011. So, therefore, it's really important that he is able to make it to Australia."

The last time members of the British royal family came to Australia was in October 2018, when the Duke and Duchess of Sussex toured in a visit that coincided with the Invictus Games.

"Of course, a lot has changed since then," Ship says.

"I think Australia is just so far away. It takes a lot of time for a King based in London to get to the other side of the world."

As expected, the King's visit has reignited the debate on whether Australia should ditch the monarchy and transition to a republic.

Late last week, the King said it would be "a matter for the Australian public to decide".

In 1999 Australia held a referendum on becoming a republic but it was defeated with 54.87 per cent of people voting against the change.

Another referendum is unlikely anytime soon after Australians overwhelmingly rejected a plan to give greater political rights to Indigenous people in 2023.

Ship says regardless of whether Australia is on the cusp of moving to a republic, King Charles has deep affection for our country.

"It's just important for him to be here, to come to Australia, a country he says he loves.

"He loves the people. It's just a shame that he can't be here for longer.

"But those are the doctor's orders."