How 2 go about his dads double life!!?

i have just found out tht my bfs dad has been livin a double life ie he has another family and its been goin on 4 ovr 10 yrs! thing is my bfs doesnt kno whereas the rest of the family does (hes the baby of the family) i feel hes gt a ryt 2 know but dont wnt to cause rifts as he has a lot more on his plate ryt now. anyone else in this situation or suggestions on what to do? thanks