Silence fell at 7:58 am (0658 GMT), the exact time suicide bombers Ibrahim El Bakraoui and Najim Laachraoui struck at Zaventem Airport on March 22, 2016.
The royal couple led hundreds of family members, rescue workers and airport staff in a solemn ceremony outside the airport, which was badly damaged in the attack.
The names of the 16 people of seven nationalities who died in the airport bombing were read out.
Later, the king and queen will travel by underground train to Maalbeek station in the city's European quarter where Bakraoui's brother Khalid blew himself up on a crowded train at 9:11 am, killing a further 16 people.
Afterwards, trams and buses will come to a halt and staff will hold a "minute of noise", in which commuters will be invited to take part "to show that they do not forget but they will stay standing against hate and terror", the Brussels public transport company Stib said.
The king and queen will then inaugurate a new steel memorial at the heart of the European Union institutions based in Brussels.
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