The Blacklist: Is Red Reddington Liz's… Mom?

Four three and a half seasons, The Blacklisthas teased us with the question of how exactly Red Reddington (James Spader) is connected to Elizabeth Keen (Megan Boone). Well, he may not be her father... but is it possible that she could still be his daughter?

One popular fan theory suggests that, yes, Liz is in fact Red's daughter -- because Red was previously known as Katarina Rostova, a.k.a. Liz's mother.

Perhaps no episode has given more credence to the theory than the fall finale, which aired on Nov. 10. Shortly after a DNA test confirmed that Alexander Kirk (Ulrich Thomsen), who was romantically linked with Liz's mother, was not Liz's father, Reddington -- in a moment alone with Kirk -- told Kirk "Elizabeth is my daughter." And then, just as Kirk was about to plunge a needle into Red's neck, Red whispered something in Kirk's ear that made him stop short. We don't know what Red said to Kirk, but whatever it was, was apparently enough to make Kirk disappear from Liz's life for good. (Whether his exit was voluntary or not remains to be seen.)
But in a later scene with Liz, Reddington reiterates his previous statement that Liz's father died when she was young, and stresses that he has never lied to her. Probably the only way that both of these statements -- Liz's father is dead; Liz is Red's daughter -- could be true is if Red is, in fact, Katarina.