Mourad Laachraoui, brother of Najim Laachraoui, beat Spaniard Jesus Tortosa 6-3 in the -54kg final in Montreux, Switzerland yesterday night.
A silver medallist at the Summer Universiades in 2015, the 21-year-old has qualified for the Rio Games in August.
Najim Laachraoui, 24, was one of the two suicide bombers who struck Brussels airport on March 22, while a third attacker blew himself up at on a metro train, with the two attacks killing 32 people.
"You don't choose your family," he told a press conference at the time, adding not to draw "any parallels" with his family who were trying to "turn the page".
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"I have no idea why my brother turned (to terrorism). We didn't see any change when he became radicalised," he said, explaining that his sporting career had distanced them over the years.
"It's crazy, they were born into the same family, they received the same education and one turns everything white and the other black, even very, very black," Mourad Laachraoui's lawyer said after the attacks.
Prosecutors have also linked Najim Laachraoui to November's attacks in Paris in which 130 people died, saying his DNA was found on a suicide vest and a piece of cloth at the Bataclan concert hall where 90 people were killed.