He performed for Allied soldiers during World War II and , accompanied on the piano by English composer Benjamin Britten , for the surviving inmates of the Bergen-Belsen concentration camp after its liberation in April 1945 .
He was the first person to perform in the Paris Opéra after the war and he went with the composer Benjamin Britten to perform for the people who were prisoners in the Bergen-Belsen concentration camp , after they were made free in April 1945 .