Hazrat Mak'hool (may Allah have mercy on him) said: "If a person marries a woman and later it is found that she is his foster sister, then if consummation has not taken place, the marriage is invalid and the wealth (dowry) will be returned. But if consummation has taken place or he has seen from her what a man sees from his wife, then the full dower will be obligatory. And if he had divorced her and given half the dower, and later the reality became known, then whatever the woman has taken she will return. The waiting period (‘iddah) will be the same as that of a divorced woman, and they will not inherit from each other."