Kate Spade began to 'distance herself' from friends before her death (Exclusive)

A source tells ET that the late Kate Spade had become withdrawn from friends and family before her death, leading many of them to worry about her well-being.

Spade was found dead in her Manhattan apartment of apparent suicide on Tuesday, and there was a note left, the NYPD confirmed to ET. CBS News reports the designer left a suicide note addressed to her 13-year-old daughter, Frances, telling her it was not her fault.

Spade was 55 years old.

"Kate definitely seemed to distance herself recently and her family was worried about her," the source tells ET. "She ventured out less and less and some friends began to wonder what was wrong. People who were used to hanging out socially with her started to worry about her because she was nowhere to be seen."

"Kate's suicide has been extremely heartbreaking and has left some friends confused because she kept a happy persona in public for so long," the source continues. "But those that knew her well, knew she suffered for years with depression."

According to the source, Spade "tried desperately to hide" her stuggle with depression.

"She truly cared about her brand and didn't want the public to know of her pain," the source says. "Kate's suicide has made some friends question what they could have done to change the horrific outcome. She definitely hid the truth of her intense suffering from so many friends, and in turn they had no idea she needed help."

The source notes that Spade's loved ones' main concern is now for the well-being of her beloved daughter, whom she shared with her husband of 24 years, Andy.

"Right now we are all looking for answers and are so worried for her young daughter," the source says. "Kate loved her daughter so much, but clearly couldn't endure the pain any longer."

Reta Brosnahan Saffo, Spade's older sister, told CBS News that she believes the designer was suffering from bipolar disorder. Saffo said that she "tried numerous times to get her help."

"It finally took its toll on her," she wrote in an e-mail to CBS News. "A very tragic and sad ending to the life of a very colorful and delightful being."

Spade's death sent shockwaves on Tuesday to her millions of fans around the world -- including plenty of celebrities -- many taking to social media to share their memory of their first Kate Spade purchase. On Wednesday, Spade's label, Frances Valentine, which she started in 2016 and named after her daughter, took to Twitter to mourn its founder.

"We are deeply saddened by the loss of our dear friend and founder, Kate Valentine Spade, who will remain in our hearts forever," the brand tweeted.

Some members of Spade family have also spoken out, including her brother-in-law, actor David Spade.

"Fuzzy picture but I love it," he shared on Instagram alongside a touching photo of the two together. "Kate and I during Christmas family photos. We had so much fun that day. She was so sharp and quick on her feet. She could make me laugh so hard."

"I still can't believe it," he continued. "It's a rough world out there people, try to hang on."

Meanwhile, Spade's niece, Marvelous Mrs. Maisel actress Rachel Brosnahan, took to Instagram to share a video of Spade joyfully dancing with her husband.

“Knowing Katy, this is how she would want to be remembered," Brosnahan wrote. "She had a light that words can’t capture but touched everyone she came into contact with. She was exceedingly kind, beautifully sensitive, insanely talented, funny as heck and one of the most generous people I have ever known. She was effervescent. “Hug your loved ones extra tight today.”

-- Reporting by Adriane Schwartz

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