mint? I am truly horrid at this.

It looks like torenia fournieri or wishbone flower. Mine self-seeds. If you've ever had this plant in your garden, it's likely the pictured plant is its offspring.

Sorry, I missed the fact that you mentioned having had torenia in the area. I can't see the bloom to which you're referring but the foliage sure looks like torenia. Does the blue bloom look like the torenia flower?

I found a site that said in nature torenia is usually blue, purple and lavender. From that base, they bred others colors. Perhaps your original torenia reverted to the "natural" color.