oh, OK he can't leave you anything that isnt his.
So if it is a half share in the house, then it is a half share in the house.
and if he mentions a house he sold ten years ago, then obviously you dont get that.
and if he says the whole house No 21,
and miss x can convincingly show that she has a 50% interest in no 21 then obviously you have a fight on your hands.
oh, and if you get everything in a will and miss X waves a marriage certificate at you (with him!) which occurred after the will was signed then you are in big big trouble........