I'm running a 3.5 D&D game where the king is dying of some sort of illness or curse, and was looking to see if there is anything RAW that could slowly kill someone who has access to the impressive curative potential of a 13th level cleric. I could always hand wave things and say it's a mystical incurable curse, but I'd prefer something that exists in the system if possible.
Must not be something that someone with access to 7th level divine spells can cure.
Must be something that would eventually prove fatal. Anywhere from 5-50 years from start to end would be good, with the longer end of the spectrum being ideal.
A curse or disease that only needs to be started and continues on its own would be ideal, but if there's a poison or something similar that could be re-administered covertly bypassing detect poison and the like, that could work as well.
Bonus points if its the sort of thing that would be hard to identify the cause of.