An escaped European shrub. There are 2 parent species:

• Tartarian: pink (sometimes white) flowers, leaves smooth beneath

• Morrow's: white flowers aging yellow, leaves downy beneath. This one's
  leaves are in between, so it's probably the hybrid, L. x bella. I'm seeing a fair number of the white ones around now, & some tinged a little pink, but this is the only really pink one I've seen. Flowers ~2 cm across. Thanks to Urtica for ID help.