This is going to drive me nuts, I remember hearing a story about a famous painter where the works from the end of his life are not considered particularly valuable because they were being forged while he was still alive, with his wife's assistance in getting his signature on blank canvases. So even in authentic signature, doesn't mean it's an authentic painting by that artist.

I thought it was Picasso, but I'm finding no reference when I read about him. Anyone know what painter it is?