Alexander Voltz, spokesperson for the Australian Monarchist League, has criticised protests against King Charles during his current visit to Australia.
Speaking to GB News, Voltz dismissed republican campaigns as "classic juvenile" and "very sleepy, not very interesting".
He said: "I think it's just a classic juvenile Republican campaign. Once again, very sleepy, not very interesting.
"I would like to hear the Republicans tell us how they're going to make our country better than what it already is.
Alexander Voltz claimed it is just juvenile
GB News
"Instead of them just attacking people like me and attacking our system of government, which we know through history works so well, what are they going to change for the better? They can't tell us.
"They've never been able to tell us, so we're just not very interested in them. And we're having a wonderful celebration for the tour."
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The comments come as King Charles III and Queen Camilla embark on their first visit to Australia as monarchs.
The royal couple arrived in Sydney on Friday evening, kicking off a six-day tour that includes engagements in Sydney and Canberra.
The tour comes amid discussions about Australia's relationship with the Crown.
The King has travelled to Australia 15 times for working trips
Getty
Recent polls show 45 per cent of Australians support keeping the monarchy, while 33 per cent favour a republic.
The Australian Republican Movement has dubbed the visit "The Farewell Oz Tour".
Voltz took particular issue with the presence of Graham Smith, Chief Executive of UK-based anti-monarchy group Republic, in Australia during the royal visit.
King Charles and Queen Camilla landed in Australia for historic tour yesterday
ReutersSmith said: "The fact that a foreign organisation is funding him with foreign money to interfere in the domestic affairs of Australia is outrageous."
He added: "His return flight should be booked as quickly as possible.
"We have no desire for this foreign interference to be going on in Australia."