Here’s a scary story with a happy ending, just in time for the holidays.

David Loewenguth, a staff member for the Hudson River Park Trust, clocked in early one morning this fall at the Gansevoort peninsula — it was 7:15a — and as he drove out of the garage in one of the park’s small vehicles, he was flagged down by parkgoers gathered in front of Little Island. A man in running gear had collapsed and was unconscious on the esplanade. David knew immediately what to do — he and his fellow staffers at HRPT are trained in CPR.

“Three people who were standing nearby said they couldn’t get a pulse, so I put him on his back and started compressions,” David recounted. In the meantime, passersby called 911 and flagged down others to help. “A guy came by — he knew CPR — and said you’re doing great, but asked if I wanted him to take over. He stepped in. Someone took his shoes and socks off. Everyone was helping out.”

Then firefighters stationed at Marine One on the end of the peninsula came out with a gurney, and then, as David said, the professionals took over. A few minutes later the ambulance arrived, the EMTs continued CPR and loaded the man into the ambulance. David and the others dispersed. But the incident weighed on his mind for days.

“At one point I thought he was breathing, but I never got the sense that he recovered,” David said. “I never knew if he survived. He had a marathon shirt on from the Southampton marathon — I was out there when that race happened. Clearly he was an athlete. How did this happen? He had a wedding band on. And I kept thinking about him — what happened to his family? his spouse?”

Weeks had gone by when he mentioned the event to a friend who is a runner — he still hadn’t been able to get the man off his mind. And a couple hours later the friend sends David a Reddit post — the man’s brother was looking for the person who saved his life. “I responded and said it was such a relief to learn he was alive. I was so happy.”

The runner, it turns out, was Tribecan Robert Sevalrud — and David was right about a lot of things. Robert, 37, does have a spouse as well as a 2-year-old son. And he is indeed an athlete — a devoted runner who was on his regular pre-work route. Robert remembers nothing of that run — his last memory from that morning is lacing his shoes. He just knows, as he said, “I owe everything to David.”

“I had to piece that morning together from all these different accounts,” Robert said. He suffered cardiac arrest, though even now the doctors are not certain what caused it. They are still investigating, but from what they can tell, he will be fine. And he now sees it as a remarkable experience.

From his brother’s Reddit post, he’s been able to meet many of the people who helped save him that day. He’s visited the firefighters from Marine One, the paramedics from FDNY EMS Station 7 who answered the 911 call, and now, David. (He’s so thankful, he said, that the Hudson River Park employees get CPR training.)

“Not everyone gets to have these kind of interactions — meet the people who saved their lives,” he said. “There have been a lot of heroes to thank.”

And he’s brought his son along with him, so the boy got a tour of the fireboat on Gansevoort, the EMS trucks at Station 7, and perhaps his favorite — the skid-steer loader the park uses called a Bobcat, which David showed him during a tour of the compost area at Pier 40 recently. (It can spin a 360, a feature the boy loves.)

“It’s been an amazing journey,” Robert said. “I’m just very thankful to be here.”