Mystery garden flower

Such a sweet flower, helps itself to the garden in quite a few spots, but I don't know its name. Can anyone help?

Activity has been curtailed by this knee/leg injury, and I've been icing it lots, and resting. Today the bruising is looking paler and the knee isn't as swollen. It'll be nice when the pain lets up, but I've got good reason to be happy that it's not worse - it could have easily been the case.