I would just explain it to her sort of how you explain it to your son, only reverse it. You tell her that she's very lucky, because she has two wonderful men who love her very much, and are honored to get to be in her life. One is her dad, "Jack", and the other is "Joe", who, while he might not be her dad biologically, that doesn't mean that he loves her any less. Explain that there are lots of things that make a family, there's "blood relation", and there's also "heart relation". You could explain that it's sort of like your son and Jack. You could then explain that your ds was conceived while you were separated from your dh, but that didn't matter to Jack, because even before your ds was born, he loved him as his son. Then you say something like "well, it's sort of like that with you and Joe - he's not your biological dad, but that doesn't mean he doesn't love you and want to be there for you".
at 3:37 AM on Nov. 18, 2010