"Mr Keating's musings clearly have no basis in fact and are just a sad feature of the latest Republican push," the Tasmanian senator said.
Keating advocated for a republic when he led the country and used an opinion piece in London's The Sunday Times to again make that argument.
He said he had no doubt that Prince Charles believed Australia "should be free of the British monarchy".
"Why would he or anyone of his family want to visit Australia pretending to be, or representing its aspirations as, its head of state?" he said.
He praised Prince Charles and said he'd always be welcome in Australia but added: "The pretence of representing this country and all that it stands for is something he and we could well do without."
Australian Republic Movement chair Peter FitzSimons said it would be great if Prince Charles would use his Australian tour to formally support a republic.
"We have heard that [he supports it] for many years and we don't doubt it's true," he told AAP. "It'd be wonderful if he'd come out and say that outright, not that we have an actual expectation of that."
He also said waiting for Prince Charles to take the throne, only to ditch him as head of state early in his reign, would be unfair.
"It is very disrespectful to Prince Charles himself, and as a nation, to say we were happy with your mother reigning over us for 80 years but we don't want you at all."
Prime Minister Malcolm Turnbull, a former chairman of the Republic Advisory Committee before an unsuccessful 1999 referendum, has previously said the issue of a republic is unlikely to be publicly debated during the reign of Queen Elizabeth.
Publicly, both Prince Charles and the Queen have stressed it's up to Australians to decide whether to follow the republic path.
Prince Charles and his wife Camilla, the Duchess of Cornwall, will be officially welcomed at a reception in Brisbane tomorrow, before opening the Commonwealth Games on the Gold Coast in the evening.
- AAP
