Board Thread:Questions and Answers/@comment-184.88.25.24-20131112235645/@comment-5102537-20131113114053

Yes, no matter how often this question is discussed, it's still all confusing.

If Morgana was Merlin's age and Merlin was about a year younger than Arthur (was this ever confirmed? I too think that Merlin was approx. a year younger than Arthur, but was it ever mentioned anywhere?), Uther had the affair with Vivienne during the Great Purge and extremely shortly after Igraine's death. I doubt that he would start such a thing with another woman when his beloved wife had just died and he was willing to start a war on magic because of her death.

This would also contradict his comment towards Katrina/the troll when he told her that he had never been with another woman ever since Igraine.

Morgana wasn't in Camelot during the Great Purge. Uther told her in season one that she wasn't there but not that she wasn't born yet back then. So assuming that she was older, she was still with Gorlois and probably Vivienne (depending on how long she lived). So would Gorlois fight at the Northern Plains while the Great Purge takes place? Unfortunately, we don't know what exactly was going on at the Northern Plains and whether or not it had to do with the war on magic.

Moreover, since Morgause and Morgana presumingly inherited their powers from their mother, Uther would have slept with a sorceress while the Great Purge and the ban of magic had already come into force. It's possible that he didn't know of Vivienne's powers (in case she was a sorceress) but quite unlikely since before Igraine's death he didn't have a problem with magic and was friends with Nimueh, Gorlois and Vivienne.

Katie McGrath said that Morgana was the eldest child, so I think when the show decided to make Uther her father and when considering the Great Purge, Igraine's death and the timeline, they left it open for debate but at the same time hinted that Morgana was actually older than Arthur.