Li-ilui nishmas R' Chaim Yissachar ben R' Yechiel Zeidel Dov on his 4th yahrtzeit
Tosfos in Moed Katan [21a ד"ה אי] implies that if a Navi tells someone that a relative is going to die - he may already start the mourning process.
A חידוש פלא!! [Thank you to my beloved friend R' Meir Zev Steinmetz Shlita for bringing it to my attention with many other sources as well].
But there is a huuuuge question: The rule is that a prophecy for something negative might not necessarily come true [נבואה לרעה חוזרת] and only a prophecy for the positive is a sure thing. So how can we be certain the person will die even if the prophet tells us so???
