The death occurred at the week end of Lady Dunsany, the art collecter and fashion connoisseur, of Dunsany Castle, Co Meath, who discovered designer Sybil Connolly.
Lady Dunsany, who was 87, died in a Buckinghamshire nursing home only six months after her husband, the 19th Baron Dunsany, passed away.
Lady Dunsany - Sheila Plunkett - had returned to her native country just over a month ago.
Educated in the history of art in Florence, she also studied in Wales where she learned to understand and appreciate modern art through artist Graham Sutherland.
In 1990 a number of Jack Yeats and van Dyck paintings were stolen in a £1 million robbery at Dunsany Castle. They have since been recovered.
Lady Dunsany gave the designer Sybil Connolly, who designed Jacqueline Kennedy's inauguration dress, her first break at a fashion show in Dunsany Castle in 1953. Ambassadors and film stars were regular guests of hers at Dunsany Castle.
She was involved in the Multiple Sclerosis Society and hosted an annual fundraiser in the castle ballroom. She was also involved in many other charitable organisations, as well as the ICA.
Born in London in 1912, she was the only daughter of Sir Henry and Lady Philips. Her first husband, Baron de Rutzsen, was killed in action in 1944 and in 1947 she married Randal Plunkett, who became the 19th Baron Dunsany.
She was predeceased by her daughter, Ms Victoria de Rutzsen, and is survived by her daughter Ms Beatrice Plunkett of Manor bier Castle, Pembrokeshire. Her step-son Edward became the 20th Lord Dunsany earlier this year on her husband Randal's death. She spent recent years in a Clane nursing home following a car accident. She will be buried in Wales on Friday.