Husband speaks out after late wife's goodbye video goes viral

After Sarah Mandel died earlier this year, the former therapist and author had her death announced in a TikTok video that has since gone viral, picking up over 2.6 million views in the month since it was posted.

In the nearly two-minute montage of video clips and photos, Mandel is seen celebrating her 42nd birthday by making a wish and blowing out a candle, doing yoga in a hospital room, holding a copy of her memoir "Little Earthquakes," singing with one of her two daughters and more.

"If you're reading these words right now, then I have died," Mandel's message began in text overlaid on the video. "I wrote this message the week I was told I had weeks to months to live."

"Only a year ago, I never in a million years would have thought I would want my death announced on social media," her message continued.

Mandel then shared how she found a supportive community on TikTok in "the toughest days" of her cancer journey and thanked others for "holding [her] hand."

"I am heartbroken that I am leaving this life well before my plans, most of all because of my girls and my beloved Derek," she wrote, referring to her husband.

She shared a heartfelt "I love you" to her daughters Sophie and Siena and ended her video with a clip of herself reading from her memoir: "We are creatures who crave certainty -- but life, it turns out, is a study in uncertainty."

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Mandel's husband, Derek Rodenhausen, told "Good Morning America" that his late wife's video came as a surprise.

"It was just so loving and beautiful and kind of just amazing… but it was kind of like, 'Wow, Sarah,' doing that in that moment, it was crazy," the 42-year-old recalled.

Rodenhausen explained that his late wife was diagnosed in 2017 with stage 4 metastatic breast cancer while pregnant with their second daughter Siena. He said there were highs and lows during her six-year battle with cancer, from learning she had no evidence of disease at one point to learning the cancer had not only returned but spread to her brain.

Throughout the process, Rodenhausen said Mandel wanted to share her deeply personal experience as a way to help others.

"I think she deeply felt that she wanted to help people," he said. "It can be [a] lonely experience to go through, having six and a half years of cancer battle, and I think what she found was that by being open about it, a lot of people would kind of then open up to her and share their experiences."

Rodenhausen said his wife turned to writing her memoir and later to social media to connect with others, especially after she decided to give up her psychology practice after her condition worsened.

"The thing that was important to her was she kind of wanted to be very transparent about what she was going through and make it real to the world, even things that, you know, sometimes, people can feel like they don't want to [share or are] embarrassed by or don't want to talk about," he said.

"It became a way to take this experience and make it less of a lonely, siloed experience but more of like a shared, whole community experience. And that I think was part of what made it really beautiful but also part of what gave her the belief that there's value in being [open] and sharing," he added.