In joint tenancy, what happens to Dave's share when he dies if his will states his nephew is to inherit it?

In the context of joint tenancy, the key principle is the right of survivorship. This means that when one joint tenant dies, their share in the property does not get passed on according to their will or estate plan but instead automatically transfers to the surviving joint tenant(s). Therefore, in this scenario, when Dave dies, his share would go directly to the remaining joint tenant, Mary, regardless of what his will states regarding inheritance.

This distinctive feature of joint tenancy is what sets it apart from other forms of property ownership, such as tenancy in common, where a deceased individual's share can be inherited as per their will. Consequently, even though Dave wished for his nephew to inherit his share, that intention is overridden by the automatic transfer of ownership to Mary, the surviving joint tenant.