Looks a bit like a lily, but I'm sure you'd have noticed a lily bulb in there. I'd give it a bit of time to show its hand, unless someone ID's it as something noxious.

the serrated leaf suggests something from bird seed, or a weed called mugwort. but not 100%

Funnily enough, I've just noticed one of these in my front garden today, coming up between poppies so I'm curious to see what it is. Hubby reckons it's a plant, I reckon it's a weed that's snuck in somehow and hid amongst the plants:))

At first glance it looked like a lily but now I think it is something I usually class as a weed and get rid of. Let it flower maybe and then decide if not sure :)

they say weeds are plants that you don't want. If you don't want it i would just just pull it out and throw it away.