I don't have a save right at the moment, but there is an event in the game where your unmarried daughter gets too frisky and has a child. One of the options you get is to acknowledge the child into your dynasty (the tool tip for the option is something like "The child William will appear in your court"). What's very strange about this is that the child won't have your daughter listed as his mother (nor will she have him listed as her son). He appears as a separate branch in the dynasty tree with no connection at all to any of your family.
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