It’s been 21 years since Pete Mercurio received a phone call that changed his life forever.

In August 2000, his then-boyfriend, Danny Stewart, called to tell him he found an abandoned baby in a New York City subway station. He thought it was a doll at first, until the baby began moving its leg. Police said the baby, whose umbilical cord was still attached, was just a few hours old. Although the newborn was immediately placed in the custody of the state while officers began searching for his biological parents, Mercurio told CNN he felt at the time that the couple would be “connected” to the baby for the rest of their lives.

He was right. Three months later, Stewart testified in a hearing on the case, and the judge asked him if he was interested in adopting the baby. Stewart and Mercurio became foster parents to the infant — now named Kevin — and adopted him in 2002. “I really didn’t know this kind of love existed in this world until my son came into our life,” Mercurio said. “Danny feels the same way.” 

Mercurio and Stewart, who married a decade ago, always told Kevin about how they became a family, and Mercurio wrote a book about their story that they read together every night. Last year, he published the book, calling it Our Subway Baby. It’s a “love letter” to Kevin, who is now 21 and a college student. Kevin’s biological parents remain unknown, but Mercurio said the family does not judge them. “We’ve always told Kevin from a very young age that he was left out of love, so that he could be found and cared for,” Mercurio told CNN, adding, “We said she left you where you could be found by us.”