Complex sentence: Nell Gwyn's father was, according to most sources, Thomas Gwyn, a captain in the Cavalier Army during the English Civil War but it is still uncertain because Madam Gwyn is rumoured to have slept with an army of men.
Split into simpler sentences: Nell Gwyn's father was, according to most sources, Thomas Gwyn, a captain in the Cavalier army during the English Civil War. However, this is uncertain because Madam Gwyn is rumoured to have slept with an army of men.