I'm fine with having a half-sibling - but I'm honestly not okay with the idea of killing Arthur off just to get that sibling into existence. Like if you want Guinevere to have had an affair or whatnot, fine by me. I made Megan since I wanted to play the daughter of King Arthur and killing him off robs a lot of that creative potential (of course, this assumes he didn't die after the kids went to the real world).