He is the father of her children and a trusted friend, no matter the fact they are divorced, and have been for two decades.
So when Bill Henrichs needed a kidney, his first wife, Mary Zeigler, stepped forward to offer one of hers.
"I care for him, still," the 62-year-old grandmother told InsideEdition.com Tuesday. "Our divorce was friendly. A good share of it was for my kids and my grandkids that we have together. And his [second] wife."
In rural Minnesota, where Zeigler and Henrichs live, people do for each other. When needs arise, everyone pitches in.
"We grew up together. We were always really good friends. It sounds kind of weird, but now I almost feel like he's my brother because we've known each other so long," Zeigler said.
They were married at 18. Henrich played the bass guitar and was going to be a rock star. "I was his head roadie," Zeigler said, laughing. "Then he had to get a real job."
They had two children, a daughter and a son. They stayed together for 24 years, but split when their children were still young. They had grown apart. Or rather, as Zeigler puts it, they grew into different people, as sometimes happens in life.
"When you're 18, you're one person. And when you're 40, you're an entirely different person," she said. "That's what happened to us. We got older and we became totally different people."
Thankfully, she said, "we were mature enough to say this isn't working but we still need to do our duty as parents." They put their children first, she said, and raised them as a family. They just didn't live in the same house.
If you were to ask her children, she said, if they would rather have parents who weren't divorced, they would say no. To them, she said, it made no difference.
And it still doesn't. Zeigler and Henrichs help care for their daughter's two children. "We talk to each other several times a week," she said.
When Henrich's kidney problems worsened, and he was in line for a transplant, she knew all about it. Some 30 people were tested as donors, and none were a good match. Zeigler knew her blood type was O, meaning she was a universal donor.
So she stepped up. "It was like feeling a tap on my shoulder," she said. She knew she was healthy and she wanted Henrichs to be able to live a full life.
"How could I not?" she said. Off she went to the Mayo Clinic, where a battery of tests proved she was a match. In October, she and her ex-husband were wheeled into surgery, where he received a gift that changed his existence.
"He is just getting better and better every day," Zeigler said. Last Sunday, she went to see him perform at his house of worship.
"It was really good to see him pick up his guitar and rock it out in the church band," she said.
As for her, she feels great. "I can't tell any difference" having one less kidney, she said. "My recovery was incredibly fast."
At the suggestion of a work colleague, she has been speaking publicly about what she did. Not for attention, but in the hope that telling her story "can help one couple be more civil to each other."
Without that civility, a divorcing couple will harm their children "for the rest of their lives," she said. Neither she, nor the father of her children, were going to let that happen.