A dog who only had five days left to live was given a new lease on life in an unexpected turn of events that has captured the hearts of millions of internet users.

The video was shared on TikTok on Saturday by the foster carer who saved his life and then became his mom, @houstonfosterdogmom. It shows the pup's dramatic change from being the "saddest dog," as she describes him in the caption, to being the happy healthy canine that he is now, finally living his best life with people who truly love him.

The poster, Claudia Papp, from Houston, Texas, told Newsweek that Chapo lived a horrible life of abuse and neglect before being saved, and healing him seemed almost impossible. However, it eventually happened, thanks to her heroic foster kittens who made it possible.

Chapo's previous owner had kept him, and five more dogs, chained up to his yard for over four years. He even left them out during Hurricane Harvey, before being reported and forced to surrender them all to the Harris Country animal shelter; it even started an animal cruelty case against him, which was later dropped.

"He is still allowed to own dogs without any government supervision," Papp said, before going on to describe the heartwrenching conditions in which Chapo was found.

"He was emaciated, dehydrated, his intestinal parasites were attacking his system. He had advanced heartworm disease, and the most alarming for me, because at that point I felt like I had seen it all when it came to animal neglect, he had the worst skin infection from a flea infestation that I've ever dealt with."

Because of his health issues, Chapo wasn't allowed to be adopted, so, as soon as he entered a shelter, he was immediately put on their euthanasia list, with a five-day deadline before being put down.

Shelters across the country are severely overpopulated and so often they resort to euthanasia, putting down dogs with fewer chances of being adopted to make space for the newcomers that arrive every day.

Of the 6.3 million pets that enter U.S. shelters, which is an average of 17,260 a day, as reported by the American Society for the Prevention of Cruelty to Animals, around 920,000 are euthanized every year.

And while shelters may think this is a reasonable decision for them, the Humane Society of the United States says that it is never humane to euthanize a dog, because, no matter what, they will indeed suffer.

Under the best circumstances, it still takes a few minutes for the pups to lose consciousness inside the gas chamber, although it often takes as long as 20 minutes. "In the worst cases, the animal is still conscious while their vital organs begin to shut down," the website adds.

When Papp saw the Facebook plea to save Chapo's life, she didn't think twice. "This indescribably powerful voice in my head said, 'Claudia, that's your next foster dog," she said.

"Every rescue group in Houston was completely full that week. But a rescue group in New York @diamondsintheruffny felt just as strongly about him as I did, and we got him on his very last day on the list."

All the other dogs that shared Chapo's abuse story also made it out alive, thanks to a couple of different rescue groups that made it possible.

However, even though he was safe, and euthanasia was behind him, Chapo's spirit was broken. Thankfully, Papp was determined to put it back together, and so she did, with an incredible amount of love and commitment, and with the help of her foster kittens.

"I've watched this boy become a dog that, four years ago, I would have never thought was possible. He's still evolving every single day, too," Papp said. "The plan was for Chapo to eventually go to New York and enter a foster home there, but Chapo never made it to New York. He was mine and I was his, and I wasn't going to let him leave me. He saved me just as much as I saved him."

When he first got home, Chapo was still depressed, but soon, Papp noticed that whenever her two kitties were around him, he instantly felt better. That is when she decided to foster sick kittens, too.

"I was willing to try anything at this point; he was just so sad all the time. It was breaking my heart and making me feel like a failure," Papp said. "After Cicely got here and was over the hurdle of her medical issues, I let her have full access to the house. That's when the magic started.

"She gravitated toward Chapo, and I realized Chapo was starting to show an incredible amount of progress. I felt like I was finally seeing his personality for the first time. While we had Cicely, that's when I decided to adopt Chapo myself."

While the kittens healed Chapo, he also mended their broken spirits just as much as they did to him. Each of these kittens, who were all ill and in need of veterinary care when Papp took them in, also gained a "dog-friendly" addition to their adoption biographies, which made finding a home for them much easier.

"I've fostered close to 120 animals. Chapo was my 48th foster dog and I had exceeded 100 foster animals by the time I got him, so dogs and cats combined," Papp said. "He is the only foster I've ever adopted or 'foster-failed.'

"Keeping any of the kittens would have kept us from being able to save another kitten. If we had kept Cicely, then this story wouldn't be what it is. Chapo's second foster kitten that you see curled up against Chapo's forehead, Uncle Violet, he wouldn't have survived if we hadn't said goodbye to Cicely."

The video quickly went viral on social media, getting viewers from across TikTok. It has so far received over 10.1 million views and more than 1.8 million likes on the platform.

Do you have funny and adorable videos or pictures of your pet you want to share? Send them to life@newsweek.com with some details about your best friend, and they could appear in our Pet of the Week lineup.