This is a volunteer that showed up in a bed in my front yard. It has an interesting cup-shaped double flower; the outer cup opens first leaving the inner cup folded up inside; in about a week the inner cup opens (you can see the inner cup beginning to open in the second flower in the picture). The lighter-colored leaves behind the flower are the ones that belong to its plant. Any help in identifying my mystery volunteer would be appreciated.
Well, not really the cup-and-saucer form (Campanula medium 'Calycanthema') where there is a flat coloured bract under the flower, as an actual double form of Campanula medium... which I have had turn up spontaneously, as well.