Mystery woman finds engagement ring on the train and turns it in ... “I told my kids that night about the ring. I wanted them to know the importance of returning something that didn’t belong to them.”

A Brooklyn bride-to-be unknowingly lost her three-carat diamond engagement ring at a subway station — then got it back two months later thanks to a kindhearted stranger.

Hager Elsayed, a teacher assistant who got engaged last May, was convinced she had lost the princess-cut ring for good in November and was considering buying a replacement.

“I felt so bad,” she said.

She was riding the N train when she noticed the ring wasn’t on her finger. She thought she’d left it at home, but after tearing the place apart, she concluded it must have slipped off her finger.

NY Post photos: Chad Rachman

FICKLE FINGER OF FATE:Hager Elsayed sports the diamond ring fiancé Juan Rivera gave her after the lost bauble was recovered in the subway.

“I guessed that since I lost a few pounds, it slipped off,” she said.

Breaking the news to her fiancé, Juan Rivera, was difficult.

Rivera, a fireproofer, worked many hours of overtime to afford the ring, and had gone to several jewelers to find the perfect choice.

“I was devastated,” Rivera said of learning the news. “I was like, ‘I’m still paying for that ring. How could you do that!’ ”

One day last month, Elsayed was at the Fort Hamilton Parkway N-train station and noticed the station agent, and realized he had been working there on the day she lost her ring.

She asked the agent, “Did anyone by any chance find an engagement ring?”

Someone had.

An elderly Asian woman who spoke no English found the ring near the MetroCard machine, said the agent, Anthony Tiralosi, 55.

“I knew it was an engagement ring because I used to sell jewelry,” said Tiralosi.

“As soon as I saw it, I knew the ring was worth at least $4,000. It was a gorgeous ring. I said, ‘Gee, whoever lost this must feel sick.’ ”

He never considered keeping it.

“It was never even a thought,” he said. “I told my kids that night about the ring. I wanted them to know the importance of returning something that didn’t belong to them.”

After providing documentation that the ring was hers — including pictures and a proof of purchase from her fiancé — she got the ring back from the MTA Lost & Found the next day.

The woman who found it remains a mystery.

“The whole moral of the story is there are still good people out there,” Elsayed said.