The couple sold their last stake in the brand in 2006 to focus on raising their daughter, Frances Beatrix Spade. In 2016, they launched a new footwear and accessories brand called Frances Valentine, naming it after their daughter, who is now 13.

Tapestry Inc, the handbag company formerly known as Coach, eventually bought the Kate Spade brand in May 2017 to tap millennials, who are drawn to the company's quirky satchels and colorful tote bags. The company's share price dipped by 1 percent to $44.68 in afternoon trading on the New York Stock Exchange.

Kate Spade New York released a statement calling the news "incredibly sad."

"Although Kate has not been affiliated with the brand for more than a decade, she and her husband and creative partner, Andy, were the founders of our beloved brand," the statement said. "Kate will be dearly missed."

The Council of Fashion Designers of America in a statement called Spade "a great talent who had an immeasurable impact on American fashion and the way the world viewed American accessories."

The New York City chief medical examiner's office said the cause of Spade's death was under investigation.

In response to the death, fans of the brand began posting pictures of their favorite handbags on social media. Chelsea Clinton, former US President Bill Clinton's daughter, was among celebrities mourning Spade.

"My grandmother gave me my first Kate Spade bag when I was in college," she wrote on Twitter. "I still have it."

Ivanka Trump, a daughter of and adviser to US PresidentDonald Trump, described Spade's death on Twitter as "a painful reminder that we never truly know another's pain or the burden they carry."

Spade told National Public Radio (NPR) last year that she first discussed starting a handbag company with Andy Spade while they ate at a Mexican restaurant in 1991.

"I said, 'Honey, you don't just start a handbag company,'" she told NPR, "and he said, 'Why not, how hard can it be?'" 

REUTERS