Since divorce wasn't allowed in most European countries, Silvia and Jean Monnet met in Moscow. In 1934, he returned from China via the Trans-Siberian railway, she from Switzerland. He arranged for Silvia to obtain Soviet citizenship; she immediately divorced her husband and married Jean Monnet.
The idea for the Moscow marriage came from Dr. Ludwik Rajchman, whom Monnet had met during his time at the League of Nations (Rajchman was connected to the Soviet Ambassador to China, Dmitrij Bogomołow). It seems that the American and French ambassadors in Moscow, William Bullitt and Charles Aiphand, also played a role.
Кстати, удивительно, что имя полпреда Богомолова некий автор вписал в википедическую статью почему-то в польской транскрипции...