By Meghan Holohan, TODAY

(NBC News) - A mother’s desperate plea on Facebook for a kidney for her 2-year-old son reunited her with a high school classmate, who was willing to donate her kidney.

The donation, which takes place today, allows the boy’s father, Ryan Wagner, to see his son, Miles, cured of a rare disease before he loses his own battle with stage 4 colon cancer.

“It means the world to me that Ryan gets to see Miles get a kidney,” donor Elizabeth Wolodkiewicz, 31, told TODAY. “I am so happy to give Ryan more time with Miles, and for him to see his baby boy get healthy.”

Wolodkiewicz went to high school in tiny Johnsburg, Illinois, with Ryan and Ashley Wagner. While they knew one another, they weren’t close. But Wolodkiewicz followed Wagner’s cancer diagnosis and Miles’ battle with a rare kidney disease on the family’s Facebook page, Team Ryan. When she realized she could help, she knew she had to do it.

“I felt moved,” Wolodkiewicz said. “It is also an honor to have been chosen to be a part of their story, especially a part of the 'good' in their story.”

New beginnings and challenges

Ryan and Ashley Wagner were high school sweethearts, dated through college and got married in July 2013. That December, they learned Ashley was pregnant. But happiness quickly turned to sadness when they received unexpected news. Ryan — who thought he had been fighting a stomach bug — learned he had colon cancer. He was 29 and with no family history of it.

“It was a huge blow. It was really hard to digest and, of course, we were really hopeful that it was curable,” Ashley, 33, told TODAY.

Only five months after the original diagnosis, they learned Wagner’s cancer was stage 4 and that chemotherapy would not cure him. People with this type of cancer typically live for about five years.

“The reality of it was too much,” said Ashley. “We have hard conversations and had to talk about things that we didn’t think we had to talk about until we were like 60 or 70."