Leith Eskandar, 22, described his younger brother as "a real, real hero", when contacted on Friday.
He confirmed to The Local that Eskandar had given his own life by putting himself in front of pupils at the school, to protect them from the masked attacker who had entered the building while they were having lessons.
"Yes, he did," the older sibling said, adding that he was spending the day with relatives still struggling to come to terms with what had happened.
"We are all destroyed, the whole family is destroyed. I can't talk right now. We are all together," he added.
Lavin Eskandar graduated from a different local high school in June this year and had been working at the Kronan school in Trollhättan for just a few months, Swedish tabloid Expressen
reported on Friday.
The newspaper said that he had a strong interest in video production and had been making music videos for Swedish artists in his spare time.
Swedish television actor William Spetz posted a moving tribute to the victim on Facebook
on Thursday night, which had been liked more than 163,000 times by Friday lunchtime.
"The price you paid was too high, it was your life, but you must know that you secured several children's futures," he wrote.
The message continued: "You were a year older than I am, you also liked to make movies (...) but Leith, I don't know if I'd have had the guts to do what you did (...) I admire you so much for what you did for those children."
Details of the teaching assistant's bravery emerged as police confirmed to Swedish media at a press conference in Trollhättan that they believe the attacker had racist motives
The Eskandar family has given The Local permission to publish a photo of their relative.