De Groot, who was an active member of the Political Party - New Guard, believed that the only person to open a Bridge of such importance should be a member of the Royal family. He was dismayed when it was announced that Premier Lang would officially open the bridge.

In De Groot's attempt to stop Lang from opening the Bridge, he arrived at the ceremony on horseback and positioned himself quite close to where the ribbon had been stretched. Just prior to Premier Lang arriving, De Groot galloped forward and slashed the ribbon with his sword. He declared the Bridge open in the name of the "decent citizens of New South Wales".

Needless to say, De Groot was arrested and taken to a psychiatric hospital. He was later declared sane, but fined 5 pounds and charged for offensive behaviour in a public place.

After the De Groot incident, the ribbon was tied together, and the ceremony went ahead.