Kate Spade's best friend speaks out about the late designer's death, legacy: 'Her spirit's here'

"We miss her every day," Elyse Arons said. "Her spirit's here."

The best friend and longtime business partner of the late fashion designer Kate Spade opened up about the iconic designer's death by suicide, saying the one question she still asks herself is "Why?"

Elyse Arons first met Spade -- whom she called "Katy" -- while they were both students at the University of Kansas and the two became inseparable ever since, working together for more than 30 years.

"I have a really hard time calling her Kate because that came about through the business," Arons told ABC News' Paula Faris. "But I had known her for so much longer than that."

Arons, Spade and Andy Spade even co-founded the last fashion company helmed by Kate Spade before her death, Frances Valentine, together in 2016.

As close as they were for decades, Arons said even she still didn't always know about what was going on in Spade's mind.

"It was tough because she didn't always say it," Arons said of her late friend's battle with depression. "She'd be sad and then ... one minute later she'd make a joke."

"We talked every day and most of the time she was very happy," she added. "But I don't know if anyone can understand the depths of depression of another person."

Arons said that in the aftermath of the tragedy, the one question she has that "won't get answered" is "why?"

"I have thought and thought and thought about it, but I think it was probably one moment of despair ... of deep sadness that she felt while she was alone," Arons said of her friend's death. "I can't answer what that was."

Arons said a large part of her friend lives on in Frances Valentine, where she worked up until the time of her death. Kate Spade even legally changed her name to Kate Valentine Spade in 2016.

"Katy had this need to create and this was it," Arons said of the company.

After her death, Arons said a lot of people have reached out to her and others at Frances Valentine, telling them how much she meant to them.

"We've had ... a lot of people write in and and talk about how she had changed their lives," she said, adding that many say: "'Please keep going and keep her designs alive and her spirit alive.'"

"That's what we're going to do," she added.

Arons said that the Frances Valentine staff is an extremely close-knit group of just 10 people.

"We miss her every day," she added. "Her spirit's here."

Every corner of their intimate New York City showroom is lined with materials that Kate Spade left behind, Arons said, including her inspiration boards, sketches and favorite items.

As the group readies up to launch a new collection, Arons quipped that if Kate Spade were still here, she thinks she would tell Arons to "take a vacation."

"I think she would be thrilled," Arons said. "I think she would be really happy."

She said she thinks that Kate Spade would want them to continue to make "other women happy."

As a friend, Arons said she thinks if Kate Spade were still here she would tell her: "'I'm okay,' she'd say. 'I'm okay, don't worry about me.'"

Today, Frances Valentine is releasing the Kate bag as a tribute to the late designer.

The bag, a handheld top handle tote in nylon with black and white cotton twill striped lining, is inspired by the original first line of handbags Kate Spade ever made.

A portion of each sale of the Kate bag -- available at Barneys Madison Avenue, Barneys.com and FrancesValentine.com -- will go to the Boys and Girls Clubs of America, in honor of Kate Spade's love and support for children's charities.

If you are in crisis, please call the National Suicide Prevention Lifeline at 1-800-273-TALK (8255) or contact the Crisis Text Line by texting TALK to 741-741. You can reach Trans Lifeline at 877-565-8860 (U.S.) or 877-330-6366 (Canada) and The Trevor Project at 866-488-7386.