Who will be given the self acquired property of my grandfather

My grandfather purchased a property(self acquired property) in 1966 on his name.my grandfather do agricultural business and milk vending businesses. My grand father has one brother.my grandfather has also got some ancestral property. In 2005, after my grand fathers death my father and my grandfathers brother have done partition of the ancestral properties by registered partition deed.after my grandfathers brothers death, his grand is claiming a share in my grandfather s self acquired property. His grand son has filed a partition suit against my father.is this suit is sustainable?.