Complex sentence: Harriet is believed to be the daughter of Sally Hemings and the widower Thomas Jefferson, who had a 38-year secret relationship beginning in Paris several years after the early death of his wife.
Split into simpler sentences: Harriet is believed to be the daughter of Sally Hemings and the widower Thomas Jefferson. It is widely believed that Jefferson and Hemings had a 38-year secret relationship beginning in Paris several years after the early death of his wife.