Check Eupatorium but would need a closer pic of the flowers and foliage to be sure. Overhead pics are more difficult since we can't see whether the leaves are opposite or alternate.

It does, thank you. Definitely Eupatorium - most likely Eupatorium serotinum. It could have been planted intentionally or seeded in. It is a lovely native so if you like it keep it, if not you could get rid of it.

Thanks, It seems to spread rather quickly. The flow bed in our backyard is covered with it.