User blog:Morganaforever/Are Arthur and Morgana siblings after all?

I'm not sure to what extent Arthur Pendragon and Morgana Pendragon can be considered siblings. To be honest, one can't even say that they are half siblings. Morgana was conceived by Uther Pendragon and Vivianne naturally, when they made love with each other. However, Uther did not take any part in conceiving Arthur. What we know is that Nimueh made Igraine conceive. Since no more details are known, one could easily say that Uther is not a biological father to Arthur but Igraine de Bois actually is a biological mother to him, since she gave birth to him. Sure, Uther can be considered a father to Arthur in many ways, since he brought him up and raised him, but maybe not biologically. However, he is a biological father to Morgana. If this is true, Morgana and Arthur are not blood-related at all.

To make this point stronger, Arthur never calls Morgana his sister, since he knows under what conditions he was conceived. However, it is uknown if Morgana knows the truth about Arthur's birth, thus calling him "brother". Even if she does know, maybe that is the reason that she is so sarcastic when she calls him brother.Also, that could be the reason that makes her strongly believe that SHE is the only Pendragon with a right to the throne: Arthur is not a true Pendragon, Uther's blood is not running within him, thus making her the only alive person with Pendragon blood.

I think It is a pretty interesting point and needs to be considered thoroughly. What do you think?