Is a man held accountable for divorcing his wife and reclaiming the dowry after discovering she is a Thayyib (previously married/not a virgin) and not a virgin, despite her admission that her family knows about it and that her maternal aunt's husband assaulted her?

First: Islamic Sharia warns against fornication/adultery, prohibits the means leading to it, and prescribes punishments for its perpetrators.

Second: It is permissible for the wife and her family to conceal the loss of her virginity, and she is not obliged to inform the husband of it, especially if it was lost due to a cause other than fornication/adultery, or if the woman who committed fornication/adultery has repented.

Third: If the husband stipulated virginity, and then it becomes clear that this condition was not met, he has the right to annul the marriage contract and reclaim the dowry before consummation, or reclaim the dowry from the wife or her guardian after consummation. However, if he did not stipulate virginity, he does not have the right to reclaim the dowry, but he does have the right to divorce. The advice is to keep her and conceal her secret if she has repented sincerely.