What is the stance on someone who has undergone gender reassignment surgery: to which gender should they belong, their old gender or their new one?

The ruling on gender reassignment surgery has been discussed in previous fatwas. However, regarding a person's lineage after the transformation, this is a complex issue among the unprecedented matters that require extensive research and collective ijtihad (definition) (independent reasoning); due to the many rulings that depend on it, such as those related to mahramiya (unmarriageability), inheritance, blood money, marriage, khalwa (definition) (private seclusion), and imamate. Therefore, we apologize for not being able to answer this question.