Not that I'm complaining! A mystery peony showed up in my backyard! I did not plant it, it just grew this year. I'm confused, though: I thought that peony grew from tubers, not seeds.
you can grow peonies from seed, it takes years and years to mature. They also will not be true to the parents, but be a hybrid of them, taking thier genetics, sometimes producting a excellent specimen, sometimes not.
However, if this is a mature plant, I would assume maybe it was planted previous to when you bought your home? unless your home was new.
Maybe it was just overlooked previously, I do not know your history at your house.
Oh, duh! It must have been hidden by the monster passionfruit vine we tore out this past year. Thanks! ;)