Then he went to work for the Queen of Sweden, who made him get up early every day to provide tutoring. Eventually he caught pneumonia from the chilly Swedish mornings, which is what caused his death. (Source)
Alternatively, he may have been poisoned. By arsenic in a communion wafer. For espousing unorthodox views on transubstantiation. (Source)
I’m not sure which of these stories I like better.