So the royal family has been assassinated (never mind how, that's above your pay grade), and many foreign monarchs are eying the throne with covetous glances. In order to avoid a destructive war of succession an heir must be found.
Fortunately the late king was a man-whore of quite extraordinary proportions, so royal bastards are in abundant supply. The council has already chosen the ideal next incumbent; the Duke of somewhere-or-other. Almost all of the other known bastards are either younger than his grace (and therefore ineligible due to the law of primo genitor) or lack anything other than circumstantial evidence of their royal parentage.
Almost all.
Five bastards, however, have seniority *and* uncomfortably concrete proof of paternity.
The players are charged with finding these fellows and knobling them or their evidence, preferably both in either order.
My problem is: What would constitute iron-clad proof of paternity in a society without D.N.A. testing, or even blood-typing?