Prince George III Bibesco died on 2 June 1941; their relationship strengthened during his illness, even though he kept his mistresses. After visiting German-occupied Paris and Venice, she made a top-secret visit to Turkey in 1943 together with her cousin, Prince Barbu II Știrbey ("Barbo Stirbey"), trying to negotiate Romania's withdrawal from the Second World War. When the Red Army invaded her country, Marthe had a passport and connections enabling her to leave on 7 September 1945. Ironically it was not Marthe but her cousin Antoine Bibesco's wife Elizabeth who was the last Bibesco to be buried on the grounds of Mogoșoaia after her death on 7 April 1945. Neither Marthe nor Antoine would ever return to Romania. When the communist government took power in 1948, it confiscated all Bibesco property. She spent the remainder of her life in Paris and England.