Overview
- His family said he passed peacefully surrounded by his wife, Anne Cooper, and their seven children.
- The Dublin-born designer dressed Diana, Princess of Wales, serving as her personal designer from 1983 until 1997.
- He was a fixture at London Fashion Week for decades, most recently showing a Spring/Summer 2026 collection in September 2025.
- Costelloe built a broad commercial footprint through a roughly 20-year collaboration with Dunnes Stores.
- Beyond runway work, he created corporate wear for major clients including British Airways, Delta Airlines and the Irish Olympic Team, while running a family-led label with his son William as design director.