>>
>>Assuming his sister is his mother's daughter of her previous marriage, she can be married either to his father or to his grandpa at some time. Then it would be a hell of relationships... <g>
>
>I don't think I thought it out as thoroughly as you did. You have to consider, amongst others, the possibility of his sister being, say, also his aunt - or even his grandma! :-)

So, was I on the right track? Or the whole story is just a joke? <g>