My question is regarding the loss of Lady Fatima Al-Zahra (PBUH) of her son who had not yet been born…

Answer

In the name of Allah, the distinguished scholar, Syed Muhammad Mahdi Al-Khurasani, addressed this matter and wrote a specific book about the son of his grandfather, Imam Ali (PBUH), Al-Muhsin. He expended great efforts, guided by the sanctity of his lineage, and felt the sorrow of his loss by his grandmother, Lady Fatima (PBUH). He and his family lived under the care of Imam Ali (PBUH), and they served the religion of his esteemed ancestor. Allah, the Exalted, granted him a long life, and you can refer to his work to find the information you seek. Wassalam.