Complex sentence: He was raised by the family nanny, Jessie Lightfoot, a woman from Cornwall, known by Francis as'Nanny Lightfoot' who continued to play a key role in the artist's development even after his exile by Captain Bacon.
Split into simpler sentences: He was raised by the family nanny, a woman from Cornwall, Jessie Lightfoot. Known by Francis as'Nanny Lightfoot', she would continue to play a key role in the artist's development even after his exile by Captain Bacon.