The Irish Georgian Society has confirmed that Desmond John Villiers FitzGerald, 29th Knight of Glin, passed away last night.
The Knight of Glin is an ancient Irish noble title handed down from chieftain times, and recognised by Irish governments.
The Irish Georgian Society said that Ireland had lost one of its titans and greatest champions of the arts and heritage.
Mr FitzGerald had been involved with the Society since its early days and had been President for the last 20 years.
''A passionate man, the Knight tirelessly worked for the future of Irish country houses, their contents, parks and gardens showing the way with the restoration of Glin Castle, and making it home to his collection of Irish paintings, furniture and the decorative arts,'' the society said in a statement.
It said that his ''unique contribution to Irish scholarship, indicated by the depth and breadth of his academic output (books, catalogues, articles), is awe-inspiring.
''Desmond was a man of immense charm as well as erudition; he cherished his beloved wife, Olda, and daughters Catherine, Nesta and Honor.
''He was always a convivial and amusing companion, never shy of expressing his opinion and even in the midst of the odd tirade the glimmer of mischief was there as his humour and love of words removed any possible sting!''
Mr FitzGerald's daughter, Catherine, is married to English actor Dominic West.