Same way as one OC I saw on devArt was apparently the biological son of Blaggut and was adopted by Cluny, unless I'm misreading it. (A) Why? B) How?) But the artist's a friend of a friend, so I don't like to point it out for fear of offending my friend because I've offended her friend ...

And the accidental-mpreg Sue was the "great-grandmother" of John Churchmouse, even though she was born during Martin's lifetime.