A dense line of MPs, aides and other parliamentary officials lined the way into the room where the prince was invited on Tuesday to speak about the abuse and bullying of children and young people online.
A large security force then ensured that those who had not managed to get a seat in the room in advance were effectively turned away.
The visit has attracted extra attention following the arrest in the United States this weekend of Harry's wife Meghan's father, Thomas Markle, who is accused of possessing child abuse material. However, no comments or statements from Meghan - who is also in Brussels - are expected.
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