My daughter isn't biologically mine, and it's time to tell her the truth, but it's complicated. Need some advice.

First I should talk about the dark days. Just over 3 years ago I and my partner were living together with a small daughter and a baby son. Then my world was thrown into a churning dark chaos. I found out that my daughter was not my daughter at all, and that I'd been deceived by my partner of 8 years. My daughter and I were especially close. My partner was occupied with the new baby, and I worked at home so I was the one who could give her the attention a toddler needs. On top of this, my mother had died a few years earlier, and I wanted nothing more than to look into my daughters eyes and see my mother looking back at me. (That thought still tinges some of the happy moments to this day). I pray that no further experience in my life comes close to replicating the torment and anguish of that period, but I'm happy to say that things for the most part have worked out well. My ex partner and I are now on amicable terms. I pay support for my son, my daughters biological father pays support for her (though he has made it clear he doesn't wish to be involved in her upbringing) and I have both children two days every week and have access whenever I want.My ex has a new long term partner who seems to be a stabilising influence on her, and who the kids are happy to call a variation of "daddy", which I have no problem with. This leads me to the issue at hand. The other day my daughter called her other "daddy" her "real" daddy. It appears my ex may have implied to her that her new partner is her biological father. This concerns me greatly. Not because I'm insecure about my daughters love for me. It's a bit because I wasn't consulted first, and a lot because I believe it's the wrong approach. This whole situation was caused by lying. I'm not going perpetuate lies to my daughter.When I think back to everything I went through, the tempest of anger and uncertainty, having to call everything you think you know about your closest personal relationships into question; I won't risk putting her through anything like that.I suspect my ex jumping the gun on this issue was more to do with getting caught off guard by a direct question than any kind of thought out strategy. Silly; it's not like we didn't know it was coming. I guess we both had our reasons to not want to think about it. I don't know how to explain to a 5 year old child that she has three fathers and that the one who is her biological father doesn't want to know her. It's not even like we can say he lives abroad or something - he lives in the same neighbourhood as they do. And there's going to be followup questions of course. Believe it or not I don't want an explanation that makes her mother sound like the huge great slut that she was (a little light-hearted humour there for you; she made some massive mistakes but she has owned them for the most part). What I mean to say is that whilst I don't want to lie, it would be spiteful (or at least unhelpful) to put my ex in a position where she has to explain her past indiscretions to the parent of every child in every school class on day one. So /r/parenting - can you help me? I think the TLDR of this is: MY ex partner and I have a 5 yr old daughter who's biological father doesn't want anything to do with her. How do we explain the situation to her honestly, in a way that will satisfy her inquisitiveness until she's old enough to understand the complexities a bit better? Pre-emptive edit here: The second child, my son, is mine; DNA test etc. via /r/Parenting http://ift.tt/2oT9Kxm