Afternoon visitor

Another afternoon on the back porch. I initially identified this afternoon's visitor as a Monarch butterfly on its way to Mexico. But, on close inspection can one see a black line crossing the postmedian hindwing?

That line is the certain giveaway for the Viceroy butterfly?  That's a line the Monarch does not have!  But which is it?  Viceroy or Monarch?

 Isn't it a bit late in the year for the Viceroy? But the Viceroy doesn't travel to Mexico, so, it would have time to loiter among the flowers here in Tennessee.