User blog comment:Aithusa07/List of Plotholes from Merlin/@comment-123.2.187.141-20150530162132

1. Morgana and Morgause are not really sisters. They can't be related by Uther, but how could they be related by Vivianne? Morgause already would have been born, and smuggled out of Camelot for unknown reasons(BTW, WHY was she smuggled out of camelot and nor morgana? Since her birth was the one that wasnt allowed, not her 'sisters'?) And Uther conceived Morgana when Gorlois was at war, so why didnt he knotice that his wife was pregnant even though he wasnt there...

Morgana and Morgause are sisters. They're related through Vivianne. Morgause is the older of the two, right? So when the original purge began although she was already born, Morgana showed no signs of magic. Morgause however, who is older, would most likely have begun her magical education, as magic hadn't been outlawed yet. It then stand to reason that Vivianne felt secure in the knowledge Uther wouldn't harm his 'apparently' non magical daughter but would have no problem executing Morgause who he had no relation to. So Morgause was smuggled out of Camelot as she was the one in danger - and that's how they're related.

Furthermore on Morgana's birth, Gorloris would have known she wasn't his. It's would, to be frank, have been obvious. But what was he going to do? Cast aside his wife (who wouldn't have had a choice in the matter because Uthers king and you can't say no to the king) and accuse his king of adultery? He was a loyal knight of Camelot and a good man. He choose to ignore Morgana's parentage and raise her as his own because to cause a fuss would be to hurt everyone around him.