Mystery plant

So, I have this mystery plant in my backyard. Here's how it came to be here.

I bought a blueberry at a local nursery last year and installed it in my garden. To say that it was a dry year would be a gross understatement. I did water my plants regularly, especially the ones that had recently been planted in the garden, and I have the ginormous water bills to prove it. As the horrible summer wore on, I noticed something strange. That blueberry bush seemed to be flourishing, while others in the area struggled. Several healthy trunks established themselves and it looked like this plant might be a winner.

Then, sometime last winter, I took a closer look at that shrub and realized that the blueberry had actually died! This flourishing shrub was something that had come from the pot that the blueberry was in and its leaves did resemble blueberry leaves, but it most definitely was not a blueberry!

I didn't know what it was. Perhaps the smart thing to have done would have been to dig it up and shred it then and there, but I hesitated. I was curious. It was a very healthy plant, but what was it? I decided to let it grow through a full cycle of seasons and see what happened. Perhaps its blooms - if it had them - would help identify it.

Around about the first of September, I noticed that the plant was full of tiny buds, so apparently it was going to bloom. I waited. And waited. And waited some more.

Finally, early this week, as I walked out my back door, this is what I saw:

The shrub which is now about four feet tall and almost that wide was completely covered in tiny, pale yellow blossoms. Furthermore, as I got close to the plant, I discovered that those blossoms were covered in tiny butterflies, bees, and even flies. The pollinators loved this plant!

The butterflies that were visiting the plant all seemed to be hairstreaks.

Several of these very colorful flies, as well as many honeybees, were also sipping from the flowers.

I believe the butterflies were Red-banded Hairstreaks, really one of the prettiest of this family of small (one-inch wingspan) butterflies.

I've identified the butterflies, but I still haven't identified the plant. I've no idea yet if it is a native plant or if it is a noxious, invasive, exotic species. What I do know is that the pollinators love it, so, for now at least, it stays. If I find out it's a thug, there will be time to rip it out this winter.

Do you recognize this mystery plant? All help in identifying it will be gratefully accepted.