Nanzi (南子) was the consort of Duke Ling of Wei (衛靈公), who had a rather unsavory reputation for political scheming and loose morals.
Zilu famously upbraided Confucius in Chapter XXVIII of Book 6 of the Analects for meeting with her when they reached the kingdom of Wei after they went into exile from the state of Lu in 496 BC. Although though there are no records of anything inappropriate occurring between them, Zilu was concerned that Confucius might become romantically involved with her or that he was attempting to enlist her help in securing a position in the government of Wei.
Appearances in the Analects of Confucius
Book 6, Chapter XXVIII
Confucius went to see Nanzi (the concubine of Duke Ling of Wei). Zilu was not happy. Confucius swore: “If I have done wrong, may Heaven punish me! May Heaven punish me!”