Flower or weed?
This massive plant appeared in the border in spring, shot up in no time with huge foliage & is now flowering. The speed & size suggests a weed to me & the slightly tatty look of the leaves & flowers. The flower is a recent picture, the foliage from a few weeks ago, it is larger still now & multiheaded in flowering.
However, I did buy some unusual plants from a plant sale that were unlabelled & I don't want to pull it out if it is some type of perennial sunflower or similar.