That's not a realistic scenario because DNA paternity tests never show "0 percent relation." Never. That's not how they work. First of all, DNA tests are never absolute. No DNA test ever gives 100% or 0% as a result. Second of all, DNA paternity tests say something like, "There is a 97.38% likelihood that the subject whose DNA was tested is not the biological father of the other subject whose DNA was tested." That likelihood does not mean that the subject is not related to the child as an uncle. You cannot draw that inference. It is not giving a percentage match of DNA but a percentage probability that the DNA tested is that of the father of the other subject whose DNA was tested, not the percentage probability that the DNA tested is that of some other blood relative. If you want to know if the other man, the first man's brother, is the father, that will require a separate DNA paternity test, for it cannot be concluded that he is not the father from his brother's DNA paternity test. That said, whoever performed the DNA paternity test would certainly know that while there is a 97.38% likelihood the subject is not the other subject's father, there is a likelihood that he's a blood relative of the child, but laboratories performing DNA tests are strictly controlled and are not permitted to editorialize in such a manner in official results, the results only stipulating to the relationship that was tested for, meaning you would never know that the tester knew that they were blood relatives, not unless you included that in the scope of what was being tested for.