Looks like a viburnum.....maybe highbush cranberry (Viburnum trilobum) or European snowball (Viburnum opulus)

Probably dropped there by a bird. You will have to remove it if you don't want the two of them growing as though stuck together.

If it were up to me, I'd pitch the spirea and keep the Viburnum. What a gift!! I agree that it's one of the "cranberry" Vibes, and it's fabulous. But then, I am kind of obsessive about Viburnums.

Thanks for the ID on yet another lousy photo. You guys are awesome. I do have plenty of spirea elsewhere, if I can somehow get it out of there. It's a shame they were planted so close together.

I'll take the Viburnam over the Spirea too. No contest.
Mike