Nicole Elliott, 24, agreed to foster Chester in late June after seeing a "hospice needed" post on an animal shelter's Facebook page.
Chester, who was about 14, was in bad shape when he arrived at a Columbus, Georgia, shelter in April. The shelter gave him a bath and a grooming.
A vet removed a large tumor behind one of Chester's legs, but more mast cell tumors soon appeared. The cancer then spread quickly through his body.
To make his final days as enjoyable as possible, Elliott spoiled Chester with a "bucket list" full of treats and activities. Here he is with Pierre, Elliott's other dog.
One day Elliott took Chester to a nearby park, where he splashed around in the water. "I have been trying to get a feel for what he is capable of," she said.
Although she had him for only a few weeks, Elliott knew it would be difficult to see Chester go. "It will be very hard, but I know the legacy he is leaving behind makes it easier," she said on Tuesday.