Re: Any advice?
While I don't have an adopted child my DH gave a daughter up for adoption in a family adoption. The girl was adopted by the maternal grandmother and she knew about that at an early age, but what she doesn't know even at 20 years old is that her sister is her mother! We had contact with the birth mother and minimal knowledge of the child till I stepped in and told the BM to stop using my DH, she was emotionally pulling at his heart and leading into needing money, so I had to stop it cold!
My point is that when this now adult finds out she will probably be lost forever which will kill my DH who has not seen her in 18 years, last thing we heard was she was sampling drugs and the adoptive mom and BM were allowing her to "explore" freely...
So tell him while you still have some control over his reactions and can help and support him.