George Totoreanu, a 25-year-old MBA student at Georgetown University, was playing video games in his home office late Saturday night when, reaching for a glass of water, he thought he saw flames flickering outside his window.

“Is that really a fire?” he asked his fiancee.

It was. Across the street from their townhouse on Sterling Terrace in Gaithersburg, a fire was engulfing another townhouse and a car in the driveway.

What Totoreanu did next, authorities said, probably saved the lives of 18-month-old twins and their grandparents: He put on his slippers and sprinted across the street in the frigid night into the burning home.

“I didn’t think about it at all,” Totoreanu said in an interview Sunday. “I just went.”

A man answered his banging on the door. Totoreanu said the man was in shock and struggled to get down the outside stairs to the street. The fire, Totoreanu quickly realized, was spreading up from the garage.

Totoreanu asked the man whether anyone else was inside. There was — his wife and two grandchildren spending the night. Totoreanu raced upstairs into the home and found her in a bedroom, holding one of the children. He picked up the other child and led everyone down the stairs.

When they reached the door, the flames were nearby and the woman was scared to go out.

“I just yelled at her and she finally came out and we all made it to the street safely,” he said.

Totoreanu, a former linguist in the Army, has been living in the neighborhood for only two months and was being treated as a hero 0n Sunday.

“We’ve gotten a lot of thank yous and welcomes to the neighborhood,” he said.

Mitch Moussa, whose parents, Antoun and Sabah Moussa, live in the townhouse, said the family was thankful for Totoreanu’s quick actions in helping save them and his nephews.

“My parents had no idea that there was something going on,” he said. “I’m afraid that by the time they realized there was something going on, we could have had loss of life.”

The fire erupted shortly after 11 p.m., beginning in the garage and probably from an electrical cause, according to Montgomery County Fire and Rescue Service spokesman Pete Piringer.

By the time firefighters arrived, everyone was out of the house, and nobody was injured. Piringer called Totoreanu’s actions “lifesaving.”

Totoreanu stood by watching as more than 80 firefighters fought the blaze in frigid temperatures and icy conditions.

He wasn’t able to fall asleep until early Sunday morning.

“I’m just glad I was able to catch it quick enough,” Totoreanu said. “Time was of the essence.”