"I wanted timelessness": The untold story of Kate Spade.

On Tuesday morning, fashion designer and businesswoman Kate Spade was found dead in her New York City apartment, aged just 55. It is believed the mother-of-one died by suicide, and left behind a note for her 13-year-old daughter.

For many fans mourning the loss of the fashion icon, Spade's tragic death serves as a poignant reminder that professional success and the outward appearance of an exceptional life doesn't shield a person from mental illness.

According to Spade's sister Reta Saffo, Spade suffered from debilitating depression for years and refused her sister and husband's persistent suggestions to pursue medical help - fearing it would damage her 'happy-go-lucky' image in the fashion world.

"This was not unexpected," Saffo wrote in an email to the Kansas City Star newspaper on Tuesday.

"She was always a very excitable little girl and I felt all the stress/pressure of her brand may have flipped the switch where she eventually became full-on manic depressive.

"I'd come so VERY close to getting her to go in for treatment... I'd spoken with them on the phone (not telling them exactly who the patient would be). They agreed to fly in and talk with her and take her with them to the treatment center.

"She was all set to go — but then chickened out by morning. I even said I (would) go with her and be a 'patient' too (she liked that idea) I said we could talk about it all — our childhood, etc. That I could help her fill in any blanks she might have...

"After numerous attempts, I finally let go," Saffo wrote.

One of the last things Spade said to her sister was about her funeral. "She said... 'Reta, I know you hate funerals and don't attend them, but for me would you PLEASE come to MINE, at least. Please!' I know she perhaps had a plan, but she insisted she did not."

So who is Kate Spade - the woman behind one of the world's most recognisable brands? And how did she climb to the top of the fashion world, while carrying a searing, quiet pain?

Katherine Noel Brosnahan was born on the day before Christmas in 1962 in Kansas, Missouri. After attending an all-girls Catholic school, she graduated with a degree in journalism from Arizona State University. It was during her time at university, while working at a clothing store, that she met her future husband Andy Spade - the older brother of comedian, David Spade.

"I was on the women's side. He was on the men's side," Kate said in an episode of NPR’s How I Built This in January of this year.  "And one day, his car broke down, and he asked me for a ride home. And we really started off as really great friends."

After she graduated, Kate backpacked through Europe, and moved to New York. She worked at Mademoiselle, a Conde Nast women's magazine that has since closed. While she promised Andy she would come back to Arizona, she fell in love with the pace of New York. Eventually, he joined her there, and together, with a third partner, they started a business in 1993 - Kate Spade.

"At the time, bags were too complicated," Kate told NPR. "And I really loved very simple kind of architectural shapes."

"I would wear these very simple shapes, none of which were famous designers. I mean, there were no names. If someone were to say, ‘whose is that?’ I'd say, ‘I don't know, I bought it at a vintage store or it's a straw bag I got in Mexico.’"

The name Kate Spade came from Kate's first name and her partner's last name - and while most people loved the name Kate Spade New York, Kate's mother hated it.

"Honestly, she burst into flames," Kate said. "And she was like, ‘but you're not Kate Spade [and] now you'll never be Kate Spade, now you've, you know, you've jinxed it. And why would you name it Kate Spade?’ And I said, well, it's my first name, his last name, and it's like Dolce & Gabbana. And she goes, ‘who the hell is that?’"

The early days of Kate Spade were a struggle, Kate told NPR. She vividly recalled being at an early trade show, and not making enough money from sales to cover the booth she'd hired. In tears, she told Andy she wanted to quit.

He asked her whether she'd had any orders of the handbags placed, and she told him she had - from Barneys and Fred Segal.

Kate remembered that Andy looked at her and said, "Katie...  You've got two of the best stores in America. Why are you crying? Let's not quit."

In 1994, Kate and Andy were married, and it wasn't until 1996 that Kate-Spade-the-brand started turning a profit.

Over the next few years, the brand grew and grew. "It was a snowball effect," Kate says. "It got a little bigger and a little bigger and a little bigger."

In 1999, Kate told The Boston Globe that the secret to Kate Spade was the balance between fashion and functionality.

"Handbags should be both. That’s what designers were forgetting," she said. "So many bags can hold a kitchen sink but they’re just big black bags."

"I was looking for something that could be less serious. More personal," she said. "I also wanted timelessness."

The signature style of Kate Spade bags - established early on - has indeed proven timeless.

In 1999, the Spades sold over half the Kate Spade brand to Neiman Marcus. The brand continued to grow, with more stores and more products - including stationery and shoes.

Then, in 2005, the couple had a daughter named Frances Beatrix Spade. At this point, they sold the rest of their business.

"I wanted to leave on good terms," Kate said. "It was the perfect time to leave, I wanted to spend time with my daughter, I’d heard so many horror stories about people who sell and then they stay and then they fight and they sue, so I thought oh, that’s too ugly for me.

"It was seamless. It was a very quiet exit."

For a decade, Kate stepped back from her place in the fashion world to raise her daughter.

In 2016, she told The Cut about her morning routine:

I normally get up at 6:30 and get everything organized by the time my daughter gets up — I’m a little OCD. I turn on all the lights, get everything going, start making breakfast. I slowly wake up my daughter up — I give her a little nudge every ten minutes. I swear to god, it’s so exhausting… I feed the dog; I feed the fish. My husband, Andy, runs to Starbucks because he doesn’t want any part of that banter. I’m in my daughter’s room going, “Oh my god, I asked you 20 minutes ago and you’re still in your pajamas.” It’s a little mini battle. She’s jealous of our dog because he doesn’t have to do anything.

In the same year, Kate and Andy launched Frances Valentine, an accessories brand. Kate legally changed her name to Kate Valentine Spade, saying at the time she wanted to show, "I’m the same person, but there’s a difference."

The way Frances Valentine started, Kate said, was very similar to Kate Spade. "It was very scrappy," she said. "We started very small and we tried not to get ahead of ourselves—I’m from the Midwest, so I’m not much of a risk-taker."

At the same time, Kate-Spade-the-brand had grown to have 315 stores globally, and to sell clothing, active wear, jewellery, home goods, eyewear, and more. It's worn by some of the biggest celebrity names worldwide, including Kate Middleton and her sister, Pippa.

Kate Spade's death on Tuesday was a shock to her loved ones and her fans, with countless tributes shared as the news broke. Among those was a photo posted by David Spade, of a smiling Kate Spade at his book signing.

"I don't think everyone knew how f*cking funny she was..." he wrote.

Indeed, there's a lot we'll never know about fashion designer, businesswoman, mum, wife, sister, daughter, friend and colleague Kate Spade.