The singer asked the audience to turn on their cellphones to light the arena, according to Entertainment Weekly, which has posted video of the moment.
"This is 'Make You Feel My Love,'" she said, introducing her version of the Bob Dylan tune, "and this is for Brussels."
Bomb attacks at the Brussels Airport in Zaventem, Belgium, and at a subway station Tuesday morning killed dozens and injured hundreds more.
In the clip, you can see the entire arena raise their phones in honor of the victims.
Model and actress Cara Delevinge, who was in the audience, took to Instagram to write, "I cried... a lot and laughed even more! A truly beautiful and inspiring show ?? thank you @adele for being you!"