E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Louis XI.s Italian astrologer. Being asked by the king if he knew the day of his own death, he craftily replied that he could not name the exact day, but he knew this much: it would be twenty-four hours before the decease of his majesty. Thrasullus, the soothsayer of Tiberius, Emperor of Rome, made verbally the same answer to the same question.
Can thy pretended skill ascertain the hour of thine own death?
Only by referring to the fate of another, said Galeotti.
I understand not thine answer, said Louis.
Know then, O king, said Martius, that this only I can tell with certainty concerning mine own death, that it shall take place exactly twentyfour hours before your majestys.