Remember in the Real Barenziah it was said that Barenziah was seduced by a bard named Nightingale (Jagar Tharn) and became pregnant of him?
Skyrim completely retcons this. Nighthingale was actualy a cover name for a famous Dunmer rogue named Drayven Indoril. Barenziah came pregnant with Drayven daughter Drulsi.
Drulsi would eventualy give birth to her own daughter, Karliah, who you might remember from the Skyrim Thieves Guild Questline.
For more info: http://www.uesp.net/wiki/Skyrim:The_Nightingales_Vol._2