(CNN)Frank Dewhurst was walking in his neighborhood when he saw the sign in his neighbor's yard.
He wanted to help a neighbor. In the process, he became the oldest living kidney donor
"I am type O and I need a kidney transplant. Please help me."
The sign gave him pause. He was type O+.
Linda Nall, the neighbor who had put it up, had been struggling with lupus since 1986, and the disease started to attack her kidneys in 2001. She had trouble getting out of her car, which Dewhurst had witnessed, and had to maintain a strict diet. He'd also seen the signs she'd put on the back of her car, as well as her social media posts.
This time, he popped by for a visit.
That was late last year. Now Nall, 72, has a new kidney -- Dewhurst's.
And Dewhurst, at age 84, is now the oldest living kidney donor in the United States.
Dewhurst is involved in the homeowner's association of their Austin, Texas, neighborhood, so when he knocked on Nall's door, she thought he was going to ask her to take down the signs, Dewhurst said.
"(She said) something like, 'That's the last thing we were expecting from you,'" he told CNN.