A fashion designer behind some of Princess Diana's most iconic looks died after falling down the stairs, an inquest heard today.

Paul Costelloe passed away in hospital on November 21, 2025, two weeks after losing balance and stumbling at his home in Putney, southwest London.

The 80-year-old had been diagnosed with cancer five months prior and the treatment had left him frail, Westminster Coroner's Court was told.

Mr Costelloe, a father-of-seven, worked as Diana's personal designer from 1983 until her death in 1997 - helping to turn her into one of the world's most stylish royals.

He also set up his own fashion house in his name and became one of the best-known names in British and Irish fashion.

The court heard Mr Costelloe lost balance and fell down around four steps at the bottom of his carpeted stairs at his home on November 7.

He had been diagnosed with acute myeloid leukaemia in June 2025 and was undergoing treatment with regular blood and platelet transfusions - leaving him with increased frailty.

Despite two cycles of treatment prior to his fall, his disease was refractory - meaning it did not go away - and he was taking G-CSF, a drug used to stimulate white blood cell growth following chemotherapy.

In July, he had to be given antibiotics after being diagnosed with neutropenic sepsis - a potentially life-threatening condition.

By October, doctors at Chelsea and Westminster Hospital who had commenced 'second line treatment' for his condition, said Mr Costelloe had become 'increasingly frail with weight loss and fatigue'.

On the day of his fall, one of Mr Costelloe's sons called 999 after hearing a noise and finding his father at the bottom of the stairs, the court heard.

Paramedics rushed him to hospital by ambulance, where he was diagnosed with a fractured pelvis and a large pelvic haematoma, fractured ribs, a spleen injury, and a bleed on the brain.

He was transferred to another hospital the following day but his condition worsened after he developed signs of a chest infection.

Despite treatment, his condition deteriorated. He passed away, surrounded by family, at 9.20pm on November 21.

In a written statement read out to the court by coroner Jean Harkin, Mr Costelloe's wife of 45 years, Anne Costelloe, said: 'We are forever grateful to the many people who supported and cared for Paul in his last weeks and days, who explored every avenue of treatment, and who never gave up hope for his recovery.

'In work, Paul was an internationally recognised fashion designer who dressed Diana, Princess of Wales, and other members of the royal family, and whose collections elevated the runways of London Fashion Week for more than 40 years.

'He cut his design teeth in Paris, Milan, and New York, but it was in his hometown of Dublin that he returned to establish his eponymous fashion house.

'Despite the responsibilities of running a global fashion brand split between his home in Dublin and his design studio in London, he was first and foremost a loving husband and father.'

Speaking to the family, the coroner said: 'Can I just say to you all, I'm really sorry for your loss.

'It's obviously a great loss to you all, and today can't be easy, having to relive those events.

'But, cast your mind back to that wonderful man that he was, that creative genius, and you have some really nice memories to take home with you.'

The cause of death given was polytrauma, resulting from a fall down stairs, acute myeloid leukaemia and advanced frailty.

In a statement after the hearing, Mr Costelloe's daughter Jessica said: 'Our focus now is on moving forward as a family and continuing to honour our father's legacy.'

Born in Dublin in 1945, Costelloe studied fashion at the Grafton Academy of Fashion Design before moving to Paris and beginning his career at the Chambre Syndicale de la Haute Couture in Paris.

He became design assistant to designer Jacques Esterel, before later moving to Milan to support Marks and Spencer in their drive to enter the Italian market.

Marks and Spencer's move into Italy was unsuccessful, but the Irish-American remained in Milan as designer for the luxury department store La Rinascente, before moving to the US, where he was appointed as designer to Anne Fogarty in New York.

He established his own label in 1979, Paul Costelloe Collections, and was soon exhibiting at fashion weeks around the world including London, Paris, Milan and New York.

In 1983, he was appointed personal designer to Diana, Princess of Wales, and continued to collaborate with her until her death in 1997.

Outfits he designed for her included a custom-made pink suit and a pink and white floral patterned dress she took to Nigeria in 1990.