This child has been through a lot with my divorce and other issues. I am asking this to try and avoid therapy and ruining this child's childhood at all costs.
Thank you for responding it tends to reinforce my original opinion that you really care what happens to this kid.
At this point, you dont have legal avenues...
MORALLY- you should accept responsibility for your part in the deception, and offer any
requested assistance.
Your honest appology to the 12year old might help - but that is moms decision now
explain that Mom and Yourself always intended to tell him the truth, but just never seemed to find the right time before you got divorced from the mother...with the lame excuse that then it was not your place to handle it anymore. If you can reassure him that you still love him the same, that this doesnt make any difference in how you see him in your heart... and at the same time give him room for his natural reaction that will be anger... possibly you can repair the damage sometime in the next 6years.
Im not normally one to jump to therapy...but if ever there was a situation ripe for it this one is...a proper therapist can give son tools to deal with the anger...and rebuilding shattered trust...get him past this crisis in one piece, maybe even stronger when he has these skills he will not need to be protected from the truth so much.
In this situation how well you respect the true parents of this child will be a reflection of how much you love and respect the child for who he really is, not just whether or not you can pretend to be his Dad... Kiddo will pick up on this right away...
Since you have the other child you cannot honorably withdraw from the situation...but you must, absolutely must, respect the wishes and the decisions made on how to handle this by the true parents...
I would say good luck, but at this point I rather think you need to be told
focus... What you want doesnt and isnt going to control the outcome.
What you do and how you act can be helpful or hurtful.
So focus on the well being of the child...
TFM