read more:The miracle twins and the unknown hero

Kris Chung walked through the front door of Toronto General Hospital at 7:00 a.m., as instructed. Over the next hour, while medical staff prepped him for surgery, every doctor who approached his bedside asked the same question: Are you absolutely sure about this? It is not too late to change your mind.

“I was very calm,” Kris recalls, more than a year removed from that April morning in 2015. “Honestly, I felt more nervous about walking into an exam than being wheeled into the operating room.”

A soldier-in-training, the 19-year-old assured the docs, again and again, he was good to go. By 8:00 a.m., the anaesthetic kicked in.

Across the street at Toronto’s Hospital for Sick Children, four-year-old Binh Wagner was waiting for what Kris had come to give: a piece of his healthy liver. By then, Binh and her twin sister, Phuoc, had triggered countless headlines around the world, their story almost too heartbreaking to believe: both girls, adopted from a Vietnamese orphanage, needed life-saving liver transplants—but their dad, a perfect match, could donate to only one. (A portion of his liver had already gone to Phuoc, deemed the sicker of the two.)

At the Wagner residence, the anonymous donor was never far from the family’s thoughts. “You’re thinking: ‘Who is this mysterious person? Is this a mother? Is this a father? Is this a young woman? A young man?’ ” Johanne says now. Even her husband—a logistics officer whose greatest gift may be his ability to compartmentalize—had an itch to know more. “What makes someone like that tick?” Michael asks.

They soon found out. Just a few weeks after Binh’s surgery, a person using an alias contacted Johanne on Facebook and provided the donor’s name (though slightly misspelled.) Adamant about maintaining Kris’s right to anonymity, Johanne didn’t even think about contacting him. In fact, she was livid someone was sharing his name because she didn’t want it to leak without his consent.

In time, though, Kris started commenting on Johanne’s social media posts and liking certain photos. Facebook chats led to email conversations, and email led to text messages. By April 2016, the one-year anniversary of the surgery, both sides knew the truth, but neither was saying. Finally, it was Kris who posed the question: “Would you like to meet?”

Since then, Kris has been able to see, up close, the fruits of his enormous gift. Binh, like Phuoc, looks nothing like the frail girl she once was, her liver ravaged by Alagille syndrome, a genetic disorder that inhibits the body from absorbing the necessary nutrients in food. They’ll be in senior kindergarten come September. “I don’t think a day goes by,” Johanne says, “that I don’t tell Binh, in private: ‘You have to say thank you in your heart to Kris.’ ”

Kris doesn’t need to hear that. Humble and soft-spoken, he brushes aside any suggestion he’s a hero, or that most 19-year-olds would never think about doing what he did. He’d much rather talk about his next initiative: Twins for Hope. (Johanne is a program director with TDH Ontario, an adoption agency that works with orphanages in Vietnam. But her charitable work is independent of her job.) Like he did that day last year—when he filled out the donor form as soon as he read about the Wagners—Kris gave his typical reply when Johanne asked him to be director of operations for Twins for Hope: “I’m in.”

“I’m glad he’s in our lives,” Michael says. “He’s got something inside that he has to help other people, and I’m not even sure he knows he has that inside. It’s almost like he is driven by a force to do these types of things.”