The questioner says that his mother gave birth to an illegitimate son who died before the questioner was born. The mother was the only person left to inherit from that illegitimate son. Then the mother died and left the questioner only. Is he (the questioner) entitled to all the property of his mother including the share she inherited from his uterine brother?
If the matter is as described by the questioner, that his uterine brother was illegitimate, and that when he died the mother was the sole heiress, she is entitled to all the property he leaves. If the mother of the questioner dies and leaves no other relatives than (Part No. 16; Page No. 512) him, all her property, including the property she inherited from her illegitimate son, will be transferred into the ownership of the questioner by means of inheritance. May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.