Board Thread:General Discussion/@comment-5674726-20150813192004/@comment-5674726-20151221211651

Remember that interview comments aren't canon. Canon is only what you see on the show itself, which leaves the question open. It is also entirely possible that the information is out of date; this interview took place in Season One, at a time when they were showing enough flirtation between Morgana and Arthur to make it sick if they planned them as siblings from Day One.

It seems more likely that there was a change of plans along the line and, if that was the case, Morgana being conceived after Ygraine's death fits better with what was established about Uther's relationship with his wife.