In 2018, Julian Gaisford-St Lawrence, former fund manager and 30th heir to Howth Castle, made a brave decision. He decided to sell the private estate, home to his family for over 800 years, to Irish investment firm Tetrarch Capital. The multi-million euro deal crossed the line last year without the price tag going public.  Not that there wasn’t any fanfare attached to the sale. There was plenty of media coverage. Howth Castle is a gem. Parts of the historic building date back to the 15th century and the 530-acre demesne includes a sunken garden designed by renowned English architect Edwin Lutyens,…