A fist-sized truffle was hidden beside a tree for Samson, the black labrador, to retrieve, directly in front of Camilla, Duchess of Cornwall.

Truffle season has long passed so the managers of French Black Truffles of Canberra in Majura Park reserved a 300-gram, $900 truffle for the photo opportunity.

With Lucy Turnbull, wife of the Prime Minister, at her side and an umbrella on her arm, the duchess smelt the truffle before Sage head chef Damian Brabender shaved it into scrambled eggs and ice-cream.

The duchess, who had expressed her fondness for ice-cream, told her minders to wait when they attempted to hurry her so she could enjoy the food.

Ms Turnbull said truffles were a family favourite and the Prime Minister had been "infatuated" with them for many years.

The duchess arrived at the farm after a Remembrance Day ceremony at the Australian War Memorial, while Prince Charles visited the National Museum of Australia.

Farm manager Jayson Mesman said he had spent weeks preparing for the royal visit and hoped it would stimulate the niche industry.

"Obviously, it's off-season, so we have been preparing the ground and infusing all the food the chef is going to prepare for today's event," he said.

"It's phenomenal to have this exposure, not just for us but for the whole industry that is rapidly growing in Australia. It's a once in a lifetime experience."

Sold by the gram, the truffles hidden underneath 1000 trees on the property fetch $2500 a kilo, with the site under 24-hour surveillance.

Two Wessex Saddleback pigs, Winnie and Piglet, looked on as the duchess was presented with a toy truffle dog by farm owner Sherry McArdle-English.

Mr Mesman trained five of his dogs, four labradors and a German shepherd, to recognise the pungency of a ripe truffle, alongside Ms McArdle-English's American cocker spaniel, Snuffle.

An excited Samson bounded into the duchess after locating the truffle

It was not the first time Mr Brabender had cooked for the royal family

"It was a fantastic opportunity to showcase cooking techniques of my own as well as truffles from the ACT, which everyone is beginning to recognise as world class," he said.

Ms McArdle-English said the duchess appeared to enjoy her visit.

"We did have a little discussion about the weather and I think she recognised these conditions are very similar to home."