Prince Charles personally intervened in a bid to save one of Northern Ireland's most important historical buildings.
A previously secret letter reveals how the future king raised concerns over Armagh Gaol.
In private correspondence to then Secretary of State Paul Murphy, he offered the services of his charities to help restore the site.
Charles also expressed interest in the redevelopment of Ebrington Barracks in Londonderry, and urged action to break the mould of housing "ghettoes" in Northern Ireland.
His lengthy missive finishes by apologising for "pestering" Mr Murphy about so many issues.
The letter, dated September 6, 2004, is among a batch of 10 sent to Government ministers. The letters to seven Government departments on subjects, including the dominance of supermarkets, badger culling and the herbal medicine sector, were written between September 2004 and April 2005.
His Northern Ireland letter was written a week after a visit to the province, and begins by referring to the "kind hospitality" he received at Hillsborough Castle.
He goes on to mention Armagh Gaol, which dates back to the 1780s and closed in 1986.
At the time of Charles' letter it had been vacant for 18 years.
He wrote: "I mentioned the issue of Armagh Gaol and suggested that my Phoenix Trust would be only too happy to help with any advice with regard to its conservation and re-use."
He cites Caterham Barracks in Surrey as a model for the development of Ebrington Barracks.
Charles concludes: "Meanwhile, this brings you countless good wishes and, I need hardly say, apologies for pestering you about so many things."