That is custard apple, also called bullock's heart. It more specific name is annona reticulata. As to the cultivar, that cannot be determined without further examination. Many of these are seedlings and have not been selected as a commercial cultivar. Be careful, this fruit, at least in S. Florida, is the wintering home of the chalsid fly. That is a very destructive pest to all annonas.

Harry

Thanks. I am in Southern California and I have no idea about the fly and effects here. I do know that plant is very healthy and now started to bear a lot of fruit and flowers.