Conversation so far:
Who is Paul Nemenyi?
Paul Felix Nemenyi was a Hungarian mathematician and physicist who specialized in continuum mechanics.
What is the significance of Paul Nemenyi to Bobby Fischer?
Peter Nicholas and Clea Benson of The Philadelphia Inquirer published an investigative report backed by detailed and compelling evidence that indicated that Bobby Fischer's biological father was actually Paul Nemenyi
How much were the monthly child support payments Paul Nemenyi made to Bobby Fischer's mother?
Paul Nemenyi made monthly child support payments to Regina and paid for Bobby Fischer's schooling until his own death in 1952.
Bobby Fischer spend time with dad?
FBI files note that Paul Nemenyi took a keen interest in Bobby Fischer's upbringing.
Did you find any interesting aspects of the history pertaining to Bobby Fischer's family in particular his sister Joan and mother Regina?
In 1938, Hans-Gerhardt and Regina had a daughter, Joan Fischer. The reemergence of anti-Semitism under Stalin prompted Regina to go with Joan to Paris.

Question: What happened in 1939?
Self-contained rewrite: What happened to Joan and Regina Fischer in 1939?