This just popped up overnight, knocking over the astilbe that was occupying the spot next to it. I just moved into the house this summer so I've had quite a few surprises but I was pretty sure everything had already come up when I spotted this guy. It looks similar to a peony but I know it can't be that due to how late in the season we are. It's planted in a fully shaded border garden against the house. I hope it's not a weed but I have no idea!