GR 12 takes you from Amsterdam to Brussels and then to Paris. The trail links 3 European capitals.

Actually, the name GR 12 is mainly used in Belgium.
In the Netherlands the trail is known as the Floris V path (LAW 1-3), a local trail linking Amsterdam to Bergen-op-Zoom.
In France the itinerary often uses other GR trails such as GR 654 and GR 1. However, the french topographic maps also mention GR 12 alongside these other trail numbers.
Also worth mentioning is that the GR 12 trail is often used as one of the popular Compostella routes leading the pilgrims from the Netherlands and Belgium into France.

At the moment it is not our ambition to fully hike this trail, although the idea certainly is tempting ... one never knows.
The Belgian part of the trail is documented in 2 separate topoguides.