What happens if a person leaves a will but the beneficiary is dead. UK only please?

Sorry if this is a bit long but hope that someone may know the answer. My grandfather died a year ago and left a will with his son, my uncle. It has just come to light that he had written an other will that invalidates the one my uncle has. In the new will everything has been left to a person that none of the family know, disinheriting his 4 children. The person named in the will has been dead for 3 years. So can my mother and her siblings make a claim or does the estate p on to the named persons family.