The Prince of Wales and The Duchess of Cornwall, who have been touring Australia for six days, joined hundreds of parishioners at St George Cathedral in Western Australia's capital in the morning.
Charles yesterday spoke of the "total horror" of the Paris attacks as he led a crowd at a beach barbecue event in a minute's silence for the victims.
The heir to the throne, an admirer of heritage architecture, later officially opened several 140-year-old state buildings near the cathedral, which have been converted into a hotel, restaurants and shops.
"So many of them convert brilliantly for other uses, so I'm thrilled to see this building being put to such wonderful use."
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The couple concluded their visit at the State War Memorial in Kings Park, days after attending a Remembrance Day ceremony in Canberra.
Charles' time in Australia was marked by revived debate about whether the country's citizens were ready to dump the monarchy, particularly after staunch republican Malcolm Turnbull became prime minister.
Turnbull, who ousted fervent royalist Tony Abbott in a party coup in mid-September, recently removed knights and dames from Australia's national honours system, calling it "not appropriate" in the modern age.