Michelle Stewart, 50, wasn’t expected to live past age 18, but she has already survived lupus, two comas, a stroke, a seizure and chemotherapy.

So when Stewart and her husband, Bob, found out her kidneys were failing in 2014, they began a desperate search for a matching donor.

“I was starting to lose hope,” said Bob Stewart, who transformed his truck into a mobile billboard advertising his wife’s blood type and organ donation need in March. Someone took a photo of the truck and posted it on Reddit. The picture went viral. At least five people came forward who ended up becoming donors for others, he said.

But the 22-year-old stranger from Denver was not among them.

“What we didn’t know was that Mason was already in the process of becoming Michelle’s donor,” Bob Stewart said.

Mason Holland saw his girlfriend’s father donate a kidney last year and was amazed at what a quick, easy process the affair turned out to be.

“After seeing him do it, I thought ‘who wouldn’t do this if they could?’ ” Holland said.

His girlfriend, Elle Powell, works for the American Transplant Foundation and matches those looking for a living donor with help in the form of personal guidance and donor searching.

When Holland tagged along to an event raising awareness for Michelle’s kidney donation in January, he told the Stewarts that he wanted to help them.

The Stewarts had heard this promise before, only to have the donor back out or end up incompatible, so they didn’t get their hopes up.

But Holland was serious and quietly went through the kidney donation process. When he saw the Stewarts at a fundraising event a couple of months later, he got to tell them the good news: He was a match.

“I think we sang all the way home,” Michelle Stewart said. “It was so emotional, so happy.”

The surgery was scheduled for the end of June.

“It was super easy,” Holland said. “I feel like there are these myths about kidney donation being this hard process for the donor, but it was totally fine.”

“His kidney was like a super star,” Michelle Stewart said, laughing.

Holland, a 6-foot-2, 22-year-old who made Denver his home a year ago, towers over Michelle as the two chatted like old friends outside the Stewarts’ home on Friday.

Bob Stewart hopes to change the sign on his truck to raise awareness for 25-year-old Kelsey Crider of Boulder, who needs her fourth kidney transplant.

But for now, instead of “wife needs kidney,” the sign reads, “wife got kidney.”

Elizabeth Hernandez: 303-954-1223, ehernandez@denverpost.com or twitter.com/ehernandez