Iconic South Australian fashion designer Harry Watt has been remembered as witty, fun and fabulous following his death overnight at age 82.

Key points: Fashion designer Harry Watt died overnight with his partner George Gross by his side

Fashion designer Harry Watt died overnight with his partner George Gross by his side The duo founded the global fashion house George Gross & Harry Who

The duo founded the global fashion house George Gross & Harry Who Watt's designs were worn by countless celebrities including Princess Diana

Watt passed away in the early hours of Monday morning with his partner and fellow fashion designer George Gross by his side.

Working alongside Gross, Watt established the famous Harry Who fashion label and spent four decades dressing some of the world's most glamourous women before retiring five years ago.

His designs were worn by celebrities including Princess Diana, Elle Macpherson, Joan Collins, Kerri-Anne Kennerley and Maggie Tabberer — just to name a few.

Author Rose Fydler interviewed Watt dozens of times for her novel 'The Untold Story of Fashion House — George Gross & Harry Who' and said he was loved by so many.

"He was a witty, original, cheeky man with a flair for style and colour," she said.

"These attributes really transferred into his fabulous clothing. He was a go-to fashion designer for thousands of women over four decades."

She said Watt would be remembered as someone who always stayed true to himself.

"[He] reached the heights of fashion, achieved his dreams, but never changed," Ms Fydler said.

"I think you could see that through his clothing which remained popular because it remained true to him."

Harry Watt and George Gross, an Australian success story

Watt and Gross opened their first store in Adelaide's Rundle Mall in 1973 and business boomed.

Six months later, they opened another store in Sydney and at the height of their success had boutiques throughout the world.

Ms Fydler described the pair's rise to the top as a "real Australian success story".

Harry Watt with author Rose Fydler. ( Supplied: Facebook )

She said even with their global success, they had a strong loyalty to Adelaide.

"Through the manufacturing plant and the factory and the offices, they employed thousands and thousands of Adelaide people over the years," she said.

"They were the last big fashion names to go offshore, they kept everything local until the very last time that it was feasible."

In the mid-1990s Gross and Watt won the contract to design the uniforms of Qantas staff — which they did for about a decade.

"That was the first time any homegrown label had won that right," Ms Fydler said.

A sad loss for the South Australian fashion industry

Prominent Adelaide fashion consultant Chris Kontos said Watt's death was a big loss for the South Australian fashion industry.

"It's really sad day and even talking about it now, I'm getting quite emotional, it really hits you that someone like him is gone … I really feel for George," he said.

"Harry was jovial and fun and fabulous and full of life."

Fashion designer Harry Watt died overnight, aged 82. ( Supplied: Facebook )

Mr Kontos said he spent two years working in their old office in Gilbert Street.

"They always threw a beautiful party and they always taught me to always have fun and make sure that you enjoyed the good bits of work," he said.

"Those boys brought a lot to this state when it came to really representing fashion in Australia and globally as well.

"Harry was always the cool rock star sort of vibe … Harry always had fun with fashion and I think that's what is amazing about what he did."

A trip to the Oscars and mingling with the stars

In an interview with the ABC in 1993, Watt and Gross spoke about their recent attendance at the Academy Awards.

Watt said when they got out of the car, there were people screaming and cheering everywhere.

"We turned around and of course it was Richard Gere and Cindy Crawford in the car that was bumper to bumper behind us," Watt said.

Watt said they got to walk into the Oscars surrounded by stars including Jack Nicholson, Bob Hope, Gene Hackman, Liza Minnelli, Angela Lansbury and Emma Thompson.

"We were very lucky that we arrived at the time when probably 80 per cent of them were arriving," he said.

The pair spoke about how they chose to manage their global business out of South Australia because they loved their life in Adelaide.

"We've got an incredible amount of fantastic friends in Adelaide," Watt said.