The youngster struggled to contain her emotions as she held a picture of her brother Mehdi Belhadj, who was killed when a former convict opened fire on shoppers in the Belgian city's central square.
Seeing her distress, Crown Prince Mathilde consoled her, placing a hand gently on the little girl's face.
Dressed in sombre grey, the royal joined her husband Crown Prince Philippe and Prime Minister Elio Di Rupo at an hour-long ceremony to remember the victims at the place where the attack happened.
Instead of speeches, a lone trumpet was sounded. Members of the public laid flowers and the Christmas market was shut as a mark of respect.
Five people died – including a 17-month old boy – in the tragedy, and over 125 were wounded.
Officials are still at a loss about the motives behind the attack.
One prosecuter said: "We are trying to find out who this person really is and how someone who did not give any sign of mental difficulties could have acted in this way."
Nordine Amrani, 33, had spent time in prison for previous drug and gun offences. He had been called in for questioning in a sexual abuse case on the day of the shooting.