Re: 4yo reveals he knows there's no grampa
There is a similar situation in my family. My son is also 4, though it is my father who is no longer part of our lives rather than my husband's. We have simply told my son the truth, or as much as I believe he can understand: "Mommy's Daddy, your grandpa, is not part of our lives." We also make sure he knows how much the grandparents he does have love him. It's hard, for certain, but it helps that my mother and my in-laws are so involved with his life. Good luck!