@Jonnasudenius, I didn't research what species might be in your country to compare, but as a bloom with 3 blue petals, it's not C. communis.

Commelina are not native to Belgium but the internet tells me that it does occur there.
Is it possible the photo might be C. coelestis?

Jonna is no longer active on this site, so I can move the photo wherever you want it to go.

deleted double post

Sorry to hear Jonna is not participating here.

I think the photo is not C. communis and offered a suggestion as to what the plant may be. The sites that I looked at were listing alien plants found in Belgium.

Since I am not positive of the correct identity, we should wait for someone with more knowledge to verify. Meanwhile I suppose the image could be moved to the generic Commelina.