Wills, promoting his charity Life Skills, which helps teenagers who leave school without qualifications, was chatting with Angela Doyle and her three daughters, who were visiting from Down Under.
Hearing the family's accents, the 27-year-old asked where they were from. Her teenage daughter replied: "Melbourne".
The Prince then said: "Melbourne – I'm visiting there soon."
Clarence House, however, played down the suggestion that he was talking about an official trip. But a royal source later conceded that there will be "a natural gap" in his training as a search and rescue pilot in early 2010 which would be the obvious time to go.
Providing both governments approve the tour, it will mark the start of a new era, in which Prince Charles' elder son will in all probability help to ease the burden of foreign travel on his 83-year-old grandmother the Queen.
There is also speculation that it could coincide with the announcement of a royal wedding and he would go with Kate Middleton as his fiancée.