Irish-American fashion titan Paul Costelloe, who was the late Princess Diana's personal designer for over a decade, has died aged 80, his family said in a statement Saturday.

"We are deeply saddened to announce the passing of Paul Costelloe following a short illness," his family said, adding he was with his wife and seven children when he died in London.

The luxury womenswear designer was one of the most prominent Irish stylists and a regular on the opening day of London Fashion Week since the inception of the show in 1984.

Born in 1945 in Dublin, Costelloe trained as a design assistant at French luxury houses in Paris before joining British retailer Marks and Spencer in Milan.

He was then appointed as Princess Diana's personal stylist from 1983 and stayed in the role until her death in 1997.

He told Irish state broadcaster that he felt he had "made it" when he was asked to be her designer.

"She was very human, she didn't act like a princess... She made a very good cup of tea and some scones," Costelloe told RTE about his most famous client earlier this year.

Known for his romantic, tailored designs, Costelloe's collections tied old-school styles with new, innovative twists, frequently featuring pops of colour, tweed patterns and florals.

Costelloe, who once compared being a fashion designer to being a tireless "athlete", presented his latest 1960s-inspired Spring-Summer collection titled "We stroll down Rodeo Drive" at London Fashion Week in September.

His brand is also a family business, with his son William the design director creating the prints and backdrops for his collections.

"My ambition is to step back from fashion eventually," Costelloe told Vogue in 2024. "To hire an old car and drive around France and paint".