Christina Summitt was bartending at a Holiday Inn when a couple came in and struck up a conversation about the paw print tattoos on her wrist.
She told them she's a dog lover and revealed that her dog Tucker just had emergency surgery after he swallowed a plastic ball.
The man then left her a $1,000 tip to help foot the estimated $2,700 bill for the surgery.
"I opened the check and I said 'Holy s—,'" said Summitt in an interview with ABC News. "I'm sorry for the language, but anyone would look at that and say it. I grabbed my sister like I was saving her from a building and made her look at it. And she said 'Holy s—,' too."
Summitt said she ran after the couple to return the money, thinking it was a mistake. But she says the man just smiled and said, "Don't you worry about it."
"There was no sweat off his back, like he just handed me a twenty," Summitt said. "I said 'I can't accept it.' And he said 'oh, you'll accept it' … And by this point in the conversation I was crying. I probably said thank you a thousand times.'"
The manager of the hotel gave the man a call shortly after the tip was left.
"I had to track him down, with all the fraud going down, I had to make sure it was a genuine transaction," said Michelle Satinik in an interview with ABC News. "We had a wonderful conversation — he said he wanted to remain anonymous. After we got all this media attention I called him back and asked, 'Still want to stay anonymous?' He said yes."
The great Dane/black Lab mix is now on medication and recovering well.
Though Summitt is still struggling to pay off all the surgical costs, she's hopeful she can do it.
"The most important part of this story is that you don't have to be well off like this gentleman to live your life this way," Summitt said. "We have to take care of each other — because if we don't, who else is going to?"
(ABC News contributed to this story)