A business associate of Otto Frank's, Mr. Van Daan was, as someone who knew him put it, "a highly intelligent and well-bred man, but in time his nervous strength gave out." This is supported by Anne's account of him in her diary; his wife appears to have been the more domineering of the two, at least during the period while they were in hiding.
Once the group was discovered, like the rest, Mr. Van Daan was taken first to Gestapo headquarters in Amsterdam for questioning, and then he was sent to the Westerbork reception camp. He, too, made the long journey by train to Auschwitz, and once there, he was separated from his wife, whom he never saw again.
Mr. Van Daan was gassed at Auschwitz, and he was seen by Mr. Frank marching to the gas chamber together with a group of other men. The exact date is not known.