The future of Britain's built heritage could be endangered by the threat to traditional building skills, the Prince of Wales has said.
He celebrated the Georgian-period Hillsborough Castle near Belfast as a "special place" with an inspiring future.
His Prince's Foundation contributed to a £24 million refurbishment by independent charity Historic Royal Palaces.
The official residence of the royal family will open to the public later this month.
The Prince of Wales also teased an artist that he always has a "slight worry" before unveiling portraits of himself.
The moment came as Charles took part in a series of engagements with the Duchess of Cornwall at Hillsborough Castle in Northern Ireland.
The couple finished the day at the royal family's official residence in the region, which has undergone a £24 million refurbishment by independent charity Historic Royal Palaces, with the unveiling of a new portrait of the heir to the throne.
Charles and Camilla were introduced to local artist Gareth Reid and his family before the big reveal.
The prince asked the family whether they were proud of him, and chuckled when they responded: "You haven't seen it (the portrait) yet."
Charles said he had had a "tiny glimpse" of an unfinished version, before joking: "There is always that slight worry when you pull the curtain down," to laughter from Mr Reid and his family.
After revealing the new painting, which depicts him sitting in a relaxed pose in a garden scene, the prince flashed a warm smile at Mr Reid before stepping back for a better look.
He nodded with approval as Camilla stepped closer also nodding, and said "well done".
The new portrait was commissioned by Historic Royal Palaces for Hillsborough Castle ahead of the official public reopening on April 18.