If a father or paternal grandfather of a child who resides in a different place marries the child to someone to become maḥram [to that person], not knowing whether the child is alive or not, then, if the marriage period is such that it is possible for the boy to derive sexual pleasure from the girl during it, what is apparent (ẓāhir)[1] is that they become maḥram.
However, if it is later realised that the girl was in fact dead at the time of the marriage contract, then the contract is void and the persons who had apparently become maḥram will be non-maḥram.