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RICHMOND HILL, Ontario — The last time Meisam Salahi talked to his younger brother, Mohsen Salahi, few words were spoken.

Mohsen, 31, and his wife, Mahsa Amirliravi, 30, were returning to Toronto from Iran, where they had been visiting relatives, and had just boarded Ukraine International Airlines flight 752 in Tehran.

Meisam, 34, called Mohsen because he was worried after hearing that Iran had fired a dozen ballistic missiles at two Iraqi air bases hosting U.S. forces.

But Mohsen was in a rush, so Meisam said he would see him when he returned or at Cestar College, where they both taught engineering.

“He said, ‘Yeah, yeah — for sure,’” Meisam recalled in an interview. “I said ‘bye.”

But Mohsen and Amirliravi never made it.

Meisam Salahi talks about his brother, Mohsen Salahi, and sister-in-law, Mahsa Amirliravi, who were killed when Iran shot down a Ukraine International Airlines plane near Tehran. NBC News

The flight was shot down last Wednesday near Tehran by Iran’s military, killing all 176 people on board. Iranian officials initially denied the country was responsible, but early Saturday, Iran's president, Hassan Rouhani, acknowledged its military had unintentionally shot it down because of “human error.” Rouhani said an investigation would identify and prosecute those responsible for “this great tragedy & unforgivable mistake.”

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Protesters in Iran took to the streets Sunday, calling on the country’s Supreme Leader, Ali Khamenei, to step down after the government reversed course and admitted it was responsible.

But thousands of miles away in his adopted country of Canada, where he and his brother had moved more than a decade ago from Iran, Meisam Salahi struggled with unsparing loss and grief. In an interview at Mohsen and Amirliravi's home in the Toronto suburb of Richmond Hill, he was still in shock.

“I can’t believe it — that I’m sitting here, in his house and he’s not here,” Meisam said. “He’s supposed to be here.”

Meisam learned about their deaths during a sleepless night last week as he worried about what might happen in the aftermath of Iran’s missile strikes. At around 4 a.m., he switched on his phone.

A friend in Iran had sent him a message on WhatsApp, asking where he was. Confused, he checked with another friend, who told him he hoped this would be the last sad message Meisam would get.

“I said, ‘What are you talking about?" He said, 'Call your mom,’” Meisam recalled. “I’m like, ‘OK.' Then my hands start shaking.”

When he got through to his mother, she was crying. At first he thought his father had died, which gave him some solace because his father had lived a long, well-traveled life. Then she said his brother’s name.

“I fell on the floor,” Meisam said, adding, “How am I going to live the rest of my life without him, without her?”

Talking with his father-in-law about what may have happened after the plane was struck brought him a measure of comfort. He thought of Mohsen and Amirliravi together, holding hands, saying “I love you” to each other.

“I think that was their last moment,” he said. “I could imagine that.”

Meisam and his wife, Kristin, are expecting a baby boy next month. Before his brother’s death, Meisam had run a couple potential names by Mohsen, who wasn’t excited about them, but he wasn’t negative either.

“He said both of them are nice — like, 'OK, interesting, and you guys decide, whatever,'” Meisam recalled.

So they did. His name will be Mohsen.

Jamie Morrison reported from Ontario and Tim Stelloh from California.