The Favor

What the message said was: "Dear Iobates, please do me a favor and kill the person who hands you this." To do so proved impossible, however, as Iobates was bound by the same strictures of hospitality as King Proetus. So instead he feasted Bellerophon for a goodly number of days and nights, until at length he announced that he had a favor to ask of him. Assuming that this had something to do with a return letter to Proetus, Bellerophon may well have been giving thought to establishing the first postal service, when Iobates surprised him with the unexpected nature of his request. Would Bellerophon be so kind as to rid the kingdom of the Chimaera?