hey anyone reading this that knows anything about fish... is it possible for two bog standard goldfish to breed and the resulting offspring to be a species of "fancy goldfish"???

we have a nice little baby goldfish in my pond with a three section tail, instead of two, is he anything special, or just some random mutant goldfish? he looks really cool, kinds like an alien. if it is a mutation, its no suprise, cos we also have an adult goldfish born with no pectoral fins, and a frog with one eye, called "one eyed jack", but thats not important