Complex sentence: His first and middle name were after his paternal great-grandfather John Wayles who, as a widower, had fathered six children by his enslaved concubine Betty Hemings, of whom the youngest was Sally Hemings.
Split into simpler sentences: His first and middle name were after his paternal great-grandfather John Wayles. As a widower, he fathered six children by his enslaved concubine Betty Hemings, of whom the youngest was Sally Hemings.