you dont

just tell him the truth, he deserves it especially if he is paying for her...something like that can be crushing and he has been mislead all the way....i am sure you had your reasons but he needs to know and if he loves her it won't matter although he will be momentarily crushed and deservedly so....

take him to maury!!!!

this seems like a very touchy issue. make sure you sit him down and be very careful and slow about saying it

what good can come from this. is there a reason you feel compelled to come clean. Ex means no longer involved.

If it has been Seven years and neither him nor your daughter know that this is the case then there would be absolutely no benefit from telling him, the only thing that could ever come from it is anger that you waited this long to tell him, resentment that now that he knows it will or could change the perceived relationship with his daughter, jealousy at the thought of you being with another man, when your daughter finds out this it could strain or destroy her relationship with you and your husband. He has raised her from birth and that is the only thing that matters, any guy can be a sperm donor but it takes a special person to be a dad.

Write him a letter, it may seem like an easy way out but at least you get your total point of view heard. Face to face sometimes there is anger and your not heard out.

Example:
Sweetheart the words I have to place in this letter may stir hurtful emotions that I wish I could prevent you from feeling, but somethings whether you are able to face them or not, you deserve to know the truth. Please accept the fact that sometimes we make mistakes in life, but how we clean them up shows maturity and understanding that what we have done is wrong; and in my heart I feel remorse for my deception and I can only hope that one day all the parties involved will find it in their hearts to forgive me and heal. I can't change my bad choice in the past but I hope the confession will begin the process making things right.