Cher was "traumatised" when she realised she would never hear her daughter's voice again.
The 64-year-old singer begged her son Chaz Bono - who was born a female named Chastity and began gender reassignment surgery around three years ago - for a copy of his old female answering machine message after becoming "hysterical" when she called and reached his new voicemail.
She said: "I was hysterical one day because I was calling Chaz's answering machine and I realized it was her old voice, and then I said, 'Chaz is there a way I can save it because I will never hear that voice again?' And there wasn't, it was gone.
"That's the most traumatic thing that has happened to me in this whole thing - hearing her voice and knowing I'll never hear it again.
The 'Believe' hitmaker also admitted she avoided seeing Chaz - whose father in the singer's late husband Sonny Bono - for a long time after he began treatment because she was so nervous.
She admitted in new documentary 'Becoming Chaz', she said: "I was so nervous. I hadn't seen her and I was putting it off.
"My boyfriend finally said, 'This is crazy, just do it.' I said, 'I'm so terrified of what will happen. If I don't recognize her, what will happen?"
Cher also admitted she still doesn't feel "comfortable" referring to her offspring as "him" rather than "her".
She added: "At some point, I'm gonna have to start calling her 'him'. It doesn't seem comfortable to me yet. Actually I just can't remember and I guess I'll start forcing myself but I'm not sure she cares."