4-year-old reunited with stranger who donated part of his liver for transplant

Kristian Vaughn stepped up to help Zanyah Brown despite being strangers.

When Zanyah Brown was 2 years old, her mother noticed that something wasn't right.

"It went from her having cold symptoms -- just runny nose, small fevers -- just not wanting to eat, things like that, to her actually being in severe pain," said Yvonne Huggins of Milwaukee, Wisconsin. "It was very scary."

Medical tests later revealed in 2015 that Brown had a rare liver condition, and she would require a liver transplant. At first, Huggins told ABC News recently, she did not have much hope.

"I'm not going to lie," the mom said. "My first thought was, 'God, this is going to take forever for her to get a liver.'"

Brown was put on the transplant list in July 2017.

In November 2017, Kristian Vaughn, a 27-year-old stranger, was determined to be a perfect match for the now 4-year-old.

Vaughn had gotten tested after learning that a family friend's son needed a liver transplant. He was a match but the child ended up getting a liver from another donor.

Vaughn then asked whether another child was in need of a transplant. The hospital alerted him to Brown, and they were ultimately matched.

The two met on Dec. 11, the night before the surgery. Only 30 percent of his liver was removed, but his partial piece of liver constituted a full liver transplant for Brown.

Their surgeons at Froedtert and the Medical College of Wisconsin and the Children's Hospital of Wisconsin ran back and forth through tunnels connecting the two medical facilities.

"It was the right thing to do," Vaughn said about his decision to donate. "All I had to do was hit the pause button on my life... for 8 weeks and then this child could just open a brand new chapter in her life because I was willing to donate and when I had that realization, I just knew that this was really, truly, the right thing to do."

Brown and Vaughn also met in March, three months after the surgery. Vaughn said he'd been told by doctors that his results were perfect and that his liver had achieved full function.

"Right there in front of me, that little girl was what life is about. It's about that joy. It's about that happiness," he said. "I feel very much privileged to have been able to be a part of all this."

Brown is doing well, and she's home from the hospital. The two continue to be in touch.

"Kristian was a blessing," Huggins said. "He changed Zanyah’s life completely."