Question:
If recently i discovered that my father is not biological father, would I still sit shiva and morn in the standatd pattern of 7 days, 30 days, 1yr?
Answer:
Regarding your question about charging for mourning in those who have discovered that their father is not a biological father, the answer is that the principle of the law is not the charge of seventy-thirty-year mourning but only on a biological father. However, if he wishes to honor him and treat him with some laws of mourning, moreover, he is also entitled to mourn him, such as when the non-biological father is the husband of his biological mother, in which case his mother deserves to be respected even after his death.
