Spencer -- the dog who became a star for cheering on runners during the Boston Marathon each year -- has sadly passed away after battling cancer. He was 13.
Spencer's owner, Rich Power, made the announcement on Tuesday ... saying the golden retriever died at their home last Friday under the care of their veterinarian.
"We are devastated to share the news of Spencer's passing,' Powers said on social media.
"Spencer has overcome some severe medical challenges over the past several years. We thought we would be lucky to have him for an extra month."
Powers -- who was gifted the pup in 2009 -- explained he was diagnosed in September 2022, and unfortunately, the cancer was inoperable.
"Spencer was not ready to give up and with the love and positive energy sent to him by hundreds of thousands of fans, He beat the odds and gave us 28 months."
Spencer went viral back in 2018 after he was seen holding a "Boston Strong" flag during a rain storm at the race -- his usual spot at the event for nine years -- and the runners always showed him love.
In fact, the Boston Athletic Association named Spencer the official dog of the marathon last year and honored him with a portrait and medal at a ceremony in Boston.
"Spencer, your spirit and determination inspired us all," the B.A.A. said after his death.
"We'll miss you, and are proud to call you a friend and forever the Official Dog of the Boston Marathon."
Spencer's owners are asking fans to donate to his memorial fundraiser ... which helps the Morris Animal Foundation Golden Retriever Lifetime Study.
The study focuses on canine health studies in the U.S. to "identify the nutritional, environmental, lifestyle and genetic risk factors for cancer and other diseases in dogs."
R.I.P.