What is this —weed— wildflower

[Rattysparklebum]

I have a small area which I leave to self seed and have visions of a beautiful wildflower garden, in reality it usually looks like an overgrown mess, every year different things pop up, any ideas what this one might be?

Just bumping this... it looks familiar but I can't think what it is. Maybe a closeup of the buds would help?

Centaurea nigra, Black knapweed, I think. If not that, then a scabious