A few facts from her early life are known. Birgit Muller was born in 1942 in Hanover, Germany. Her mother, Ingeborg Muller, and her father divorced when Birgit was young. In 1946, she married Baron Henrik Gábor István Ágost Freiherr Thyssen-Bornemisza de Kászon et Impérfalva, a geophysicist and eldest son of one of the Continent’s richest men. By then, the young baron, who went by the name Stephan, had embroiled the family in two international scandals — first by eloping with a teenage bride in Texas and then by killing another paramour in a shooting accident in Hungary. A rare...