What an awful and unhelpful comment. It is more likely that the mother has poisoned the son against his father. What he can do is discipline his child and build relationship if and when they are together. However, children are apt to believe their primary caregiver and also use that conflict to have power over whichever of their parents does not cede to their every demand. Sometimes, these children cannot see the truth of a situation until well into adulthood, and you have to let them go.