The older brother of the little Syrian boy, who was pictured sitting in an ambulance dazed and covered in blood after an air strike, died from wounds sustained in the attack on the family's apartment.
Ali Daqneesh, 10, was wounded in Wednesday's air strike, according to UK-based monitoring group the Syrian Observatory for Human Rights, and a witness who was present at the time of the death along with the boys' father.
"He was martyred while in hospital as a result of the same bombardment that their house was subjected to," said Besher Hawi, the spokesman for the local council of Aleppo. He had internal bleeding and organ damage, doctors told the witness.
Ali, 10, was not with his younger brother at home but playing with friends out in the street when the bomb fell on Wednesday. While his family sustained minor injuries when their home collapsed he was more seriously hurt in the blast.
"He stayed in the intensive care unit for three days," he said. "His general condition was unwell because he stayed behind in the rubble for a long time," unlike his brother, five-year-old Omran.
The haunting images of five-year-old Omran, sitting in an ambulance after the attack, his face, arms and legs caked in blood and dust, have reverberated around the world, becoming a symbol for the suffering of children in Syria's brutal five-year conflict.
In video footage from the incident, Omran is seen quietly staring into space before raising his arms to touch his bloodied forehead, then looking at his hand and wiping it on the orange seat.
Fighting and air strikes in and around Aleppo have killed 448 civilians so far this month, the Observatory said.
Rebels, supported by the United States, Turkey and Gulf Arab nations, have been fighting since 2011 to oust President Bashar al-Assad, who is supported by Russia and Iran. Russia began air strikes last September.
More than 290,000 people have been killed since Syria's conflict broke out, including nearly 15,000 children.
Regime warplanes, backed by Russia's air force since September 2015, bombard the eastern districts while rebel groups fire rockets into the west.
Of the estimated 250,000 people still living in the eastern parts of the city, 100,000 are children, according to the UN's children agency UNICEF.