Almost perfect Answer, except that -

Paul Nemenyi is a Father,

so actually, Robert Paul Nemenyi is Booby Fisher, 100%, as Paul Nemenyi was sending child support to Regina Fisher until his death, and even after that, Regina sent letter to his family, and asked them, if he left anything to Bobby on his will?

They met at 1942, outside USA at first time...

FBI also sure confirmed it Father's Paternity, as they always looks for her back, because, she got a medical training... at 1 Moskow Medical Institute, before ww2, and she was blacklisted as an Activist, and as potential spy... Long story...