The father is related to him ie a cousin etc. it depends on how many markers...keep in mind the percentages increase the likelihood of a relationship. And theoretically only half the DNA come from each parent. Are the mother and alleged father even distantly related?
If a man is closely related to the father of a child, he could have DNA markers like those of the child even though he is not the father. This therefore means, that a wrong identification can be concluded. The men can be brothers or identical twins.