Barbara Radziwiłł's ghost — summoned by a panicking king with a literal magician

this one's documented at the level of actual royal court chronicles, which is why it creeps me out more than haunted-castle stuff. Barbara Radziwiłł, second wife of King Sigismund II Augustus of Poland-Lithuania, dies 1551, young, suspected poisoning (everyone blamed his mother Bona Sforza). the kin……