[@Obscene Symphony]
Rumors? Perhaps something like this will do, though I apologize Smarty that it does involved the king as well.

She's a bastard born in Dorne, a whore they say with little care for the rest of the realm. Her appearance here, and suddenly being taken into the castle by her father even when he has the children to support the Targaryen rule, why would he bring in an outsider? The peasants say that he doesn't believe his son can rule; that she's a dragon where his wife's children are not. 

People are always concerned with who another is, and regardless of how well one hides the facts, bits always make it through. So where does Manasa go when she vanishes for weeks at a time? She does not appear sickly or frail as they claim, but she was once spotted in her bed, sleeping for three days straight without any prior injury.