Is the apartment considered a gift to the deceased grandson, owned by his heirs, or does it still belong to the grandfather who gave it?

If the grandfather gifted the apartment to his grandson while he was in good health, and the grandson took possession of it, then its ownership transfers to the grandson. The grandfather is permitted to revoke the gift as long as it has not left the grandson's possession. However, since the grandson died before the grandfather could revoke it, the grandfather no longer has the right to revoke it, and it becomes the property of the heirs. But if the grandson did not take possession of it and died, and the apartment remained in the grandfather's possession, then the gift is nullified and returns to the grandfather. It is necessary to refer to the Sharia court to determine the matter.