Which Belgian queen was a close friend and correspondent of Albert Einstein?

The Belgian queen who was a close friend and correspondent of Albert Einstein was Queen Elisabeth.

Elisabeth of Bavaria, Queen of the Belgians, met Einstein in Brussels during the 1927 Solvay Conference on quantum physics. She and Einstein shared an interest in music, and he sometimes visited her at Laeken, where they talked and played violin together. Her husband, King Albert I, also took part in discussions with Einstein about European affairs.

After Einstein left Europe for the United States in 1933, the friendship continued through an extensive correspondence. Their letters dealt especially with music, peace, politics, and the anxieties of the age. The correspondence lasted until shortly before Einstein’s death in 1955.

She is sometimes confused with later Belgian queens such as Astrid, Fabiola, and Paola. Elisabeth was queen consort from 1909 to 1934 and then queen dowager. She remained an important patron of music, science, and the arts for the rest of her life.