Hi Elizabeth. I remember reading a blistering argument in the letters page of the London Review of Books between the art historian Charles Hope (who doubts the authenticity) and the former owner of the painting, dealer Robert Simon. The argument went on for several weeks, with others chipping in too. There was a whole issue around whether the painting should have been shown at the NG in London as an "authentic Leonardo" when it was still being touted for sale. Hard to know the truth looking in from the sidelines, but where money is involved, I suppose anything is possible.