Earl O’Neill succeeded his father in 1798, and about ten years later, entrusted his ideas for a further expansion of the Castle, to the famous architect Nash. Regent’s Street, Regent’s Park, Carlton House Terrace, and Buckingham Palace were all designed by Nash, the leading architect of his day. He built both in the Classic style, as at Buckingham Palace, and in the Gothic castellated style, as at Shane’s Castle. The main object of the plan was to give the house a southern aspect, whereas, previously, it faced east.
In 1816, only the terrace and Conservatory had been completed, when the main block of the Castle was destroyed by fire. Legend attributes the cause of the fire to the Banshee. Normally, a room was kept empty for her use, but on this occasion, a large house party needed every room. She was so angry at finding her room occupied that she set the Castle on firm. In fact a jackdaw's nest caught fire at the top of the chimney, unused for many years, eventually crashing down into the room.
The terrace, even though no longer surrounded by water, is a permanent reminder of Nash's scale of building, and the ast uncompleted rooms would have commanded a fine view over the Lough. The completed conservatory is an exact copy of the one Nash built for himself at East Cowes Castle, Isle of Wight. Today, it houses one of the finest collections of Camelias in the United Kingdom: they are over 100 years old.