Shazmo, part of me also thinks exactly the same thing.
I am putting myself in the son's shoes. If I were him, how would I feel about being told? I think once over the shock, it wouldn't be too bad, because he'd experienced two parents bringing him up with love. Then as an adult he could decide whether to do some searching or accept that the man who'd always been good to him hadn't let him down. It might, as others have mentioned, help him appreciate our friend a bit more.
Or of course, there could be profound psychological trauma!
Would our friend feel guilty rather than relieved once he'd told him, and feel awful for letting down his late wife?
Who'd be an Agony Aunt! 
Hysteroscopy using spinal block/epidural


