Christine Royles, a 24-year-old in Portland, Maine, was diagnosed with stage four kidney failure in 2013. She's been waiting for a transplant for about a year-and-a-half.

The problem is she has type-O blood, where you can donate to anyone, but only people who also have type-O blood can donate to you.

So she started feeling desperate recently, and decided to up her chances of finding a donor by advertising on the back window of her SUV.

(Christine Royles)

She wrote, "My two-year-old son needs a healthy mom. Looking for a type-O blood kidney." Then she listed her number and a 30-year-old named Josh Dall-Leighton decided he'd donate, even though they'd never even met.

Josh is married with three kids, two of them are ten-month-old twins, and one has a brain condition. So he says the part about her son is what caught his attention. The transplant is next month, and he'll have to take about a month off work to recover.

Someone set up a GoFundMe page to raise $6,000 for him and it's already raised more than forty grand.