We're no strangers to monarch butterflies here at Teach Éan, and do our best to attract and support them on our tenth of an acre; at last count, I believe Jessa's garden list was up to 97 species of Nebraska- or at least regionally native wildflower species, including at least six milkweeds. We've had several wildflowers blooming well into October, but the most popular with the monarchs were goldenrods and asters, especially aromatic and New England asters.
This butterfly showed up about two weeks ago and appeared at first to be a late monarch, but both Jessa and I noticed some differences, and (thanks to her smartphone photo) were able to identify it as a queen butterfly, Danaus gillipus. (The proper monarch is D. plexippus.)
The queen is not a rare butterfly, but an uncommon find here. The queen is a predominantly tropical species, more typically found in the southern tier of the U.S. So an "accidental", but a nice bonus for Jessa's gardening efforts.