Willowherb, Epilobium. I'd guess E. ciliatum.

You're absolutely right! I found pictures online for willowherb and they match the plant in my yard. From what I read, it's a very invasive weed. I'd better pull it out before it takes over my garden!

It's already released some seed. Keep an eye out for seedlings.

When you pull it, bag it in the trash To contain the seeds that haven’t released.

For future plant IDs there is a forum here on Houzz called Name that Plant that is just for plant ID.

Name that Plant