Mexican Butterfly Weed, also known as Scarlet Milkweed. To be very specific, the Latin for it is: Asclepias Curassavica.
I grew it a few years ago, and eradicated it when it got a little out of control. Now out of nowhere this volunteer comes up, and Im in love again. Better management of spent flower heads will prevent it over populating the garden again.
Heres hoping lots of butterflys will come to enjoy it, and maybe even lay thier eggs. Fingers crossed!