Spencer, a beloved dog who cheered on tens of thousands of runners at the Boston Marathon over the years, died on Feb. 17 following a second bout of cancer, owner Richard Powers confirmed to "Good Morning America."
The 13-year-old golden retriever, a trained therapy dog through the Pets and People Foundation, had won over the hearts of athletes and fans online for holding a bright blue "Boston Strong" flag near the start of the race since 2015.
Runners loved seeing Spencer carrying a flag, Powers, a photographer and owner of The Henry Studio, said, but things really changed in 2018, when the marathon fell on a cold day with icy rain.
"I outfitted him in my rain jacket, and we went and we stood in our usual spot, and the response of the runners was just amazing," Powers said. "I took a small video with my phone and I just uploaded it to social media and then my phone got wet and died. I didn't know it would take off the way it did. But then it really, really took off."
Spencer was named a VIP or "very important pup" and became the official dog of the 126th Boston Marathon last year.
During the pandemic, Spencer was diagnosed with cancer for the first time.
"In 2020, he had some serious, serious health issues where he almost died. They took a three-and-a-half pound tumor out of him," Powers recounted.
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But it was also during the pandemic that Spencer became the star of Powers' "pupdate" calendar, alongside his niece, another golden retriever named Penny. Some of the proceeds from the calendar sales and an online fundraiser now aim to raise money for canine cancer research.
Spencer was a "happy-go-lucky dog" and an "angel on Earth," according to Powers, who also said he meant everything to him and his wife and they cherished their time with him, especially in his last few months, after his cancer returned a second time.
"He was our world. He was everything. He and Penny -- they were just wonderful dogs and each of them were too good not to share, and so that's what we did," he said.
Powers told "GMA" he wants Spencer to be remembered as "a symbol of hope" and for his work as a comforting therapy dog at hospitals, schools, colleges and assisted living facilities.
"He really was attuned to other people in wanting to help and giving hope," Powers said.
"He beat the odds. So he's a symbol of hope and proof that you can beat the odds and you can do more than you think you can," he added.