Sorellanza Stregonesca - Wyrd Sisters, by Terry Pratchett (1988, UK)

Verence, king of Lancre, is killed by the duke and his wife. But he doesn't properly disappear: he becomes a ghost.
Granny Weatherwax, Magrat and Ogg, although they really would like to comply with the rule forbidding witches from getting involved, save the young prince, who'll grow up as an actor.
But fate is powerful, and so are witches. Although the court fool...
Hilarious and genial, as all the Discworld books are.