'I am not a subject' is what a girl had written on a little cardboard sign in front of the Amsterdam royal palace during the inauguration ceremony of the Dutch king 10 years ago. She was arrested, driven around for hours until the ceremony was over, and later released without charge.

I saw it on TV. It's what got me into republicanism.

'They're arresting everyone'. I had gotten up early last Saturday to cover the #NotMyKing protests for the Alliance of European Republican Movements when a volunteer pulled me aside. The key organisers of the rally, the ones with all the media contacts and access to the social accounts of Republic, had been stopped by the police on a backstreet.

We ran towards the street where a large police force circled six men and women in yellow shirts. I took out my camera and started filming.

'In a democracy, we shouldn't be arresting people for peaceful protest,' one of Republic's board members told a police officer leading the arrest. 'I'm not going to get into a conversation like that, okay' he responded, 'they're being arrested, end of.' Not much later, the whole core team was handcuffed and led to police vans to be taken to the station.

About 15 minutes later, the first reporters arrived.

After I posted the video of the arrest on Twitter, news media picked it up worldwide. CNN, Washington Post, The Guardian, Newsweek, Al Jazeera, Republic World, ARD, Financial Times, just to name a few. 'They're being arrested, end of' caused a lot of outrage.

The core team of Republic was released only just before midnight. Again, away from the cameras, all of their phones confiscated.

I personally don't believe this arrest was a 'mistake'. Republic had been in contact with the Metropolitan Police for months; they have a strong track record of peaceful protests, and all the police found on them that day was a bunch of yellow placards saying 'Not My King'.

But whatever the intent behind the arrest was (and keeping the core team locked up until the royal PR show was over), it didn't do much good for the monarchist cause. Millions saw the video, many started questioning the forced role of the monarchy in society, and thousands signed up for Republic.

READ MORE: Arrests of peaceful protesters. Republic's response.

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Bram van Montfoort is the campaign director for the Alliance of European Republican Movements. This column reflects his personal views.