The affair with Briand lasted until May 1919. In 1915 Briand wrote to her that, having come to know and like Prince George, he felt guilty about their secret passion. George tried to persuade him that Greece, officially neutral during World War I but whose King was suspected of sympathy for the Central Powers, really hoped for an Allied victory: He may have influenced Briand to support the Allied expedition against the Bulgarians at Salonika. When the prince and princess returned in July 1915 to France following a visit to the ailing King Constantine I in Greece, her affair with Briand had become notorious and George expressed a restrained jealousy. By December 1916 the French fleet was shelling Athens and in Paris Briand was suspected, alternately, of having seduced Marie in a futile attempt to bring Greece over to the Allied side, or of having been seduced by her to oust Constantine and set George upon the Greek throne.