I don't know when it would have been the right time to tell my children (they are my children not my husbands). Our relationship with C has developed over four years and early on it didn't seem necessary to say anything because we didn't know if it was going to last. For the last couple of years we have been increasingly open about C being part of our lives and most of our friends know about it.
My children are 25, 22 and 19 and I have tried to tell them. The present situation is that the 25 year old gets on very well with C and enjoys spending time with her; the 22 year old closes down every conversation, refuses to even talk about C and will not meet her and the 19 year old will talk about her but doesnt want to meet her. He takes the view that he doesn't like me to get too involved with his friends/girlfriends and he doesn't want to meet my friends. I have tried a number of times to gently raise the issue with my daughter because it makes me sad that she is clearly unhappy with it, but trying to discuss it just upsets her. I have decided that it is better to focus on having a good relationship with my daughter, I make sure that I spend time with her and I try to show her that I am very happy with my life. I hope that in time she will become more comfortable about C.