What is the ruling if a man takes back his wife, but she does not know, and then she marries another man?

The Shaykh : This is a man asking. He says that he divorced his wife with a revocable divorce and took her back before the waiting period ended, but neither she nor her guardian knew until she married another man after the waiting period had ended. Then her first husband claimed that he had taken her back and brought witnesses to that effect, stating that he had taken her back. I say in answer to this that the matter must be referred to the court, because the issue is not simple at this point. The woman has already married, and the marriage of the second husband cannot be invalidated merely by a fatwa presented to us. It is necessary to go to the court, and the second husband must wait until the matter is concluded by the Shari'ah court.