ComeOnGran,I have a Transgender member of the family.Once the initial surprising shock has settled you will find it easier to deal with.I would advise not to dismiss your DS feelings,liston to what he is saying,take time to digest it all.I assume that even saying 'he' is wrong.Our family member who came out as "He" and changed his name and had surgery is now living a great life as a man,has experienced alot of positivity and to be honest you wouldn't know he wasn't born a "he" it takes time to get used to the new pronouns.Before a Transgender person can get any hormone treatment they have to have several,very indepth,appointments with experts.If someone is living in the wrong skin,try to imagine how impossible hard it must feel,and how incredibly hard it is for them to tell anyone how they feel.Be kind,be patient,and be there.Once our family member chose a male name and told us that's what he wanted to be known as,there was no looking back.Even the elderly members of the family took it in their stride.Apart from one work colleague,he has had no issues or negativity.Now it just feels like he has always been this way.We are now 6 years with the new way of life for himself and it's not an issue at all.You can find help and support online and there has been many documentaries with Transgender families that might help.I thought I would almost morn the loss of the beautiful girl we used to have,but now she is a "he" and is happy and honestly to us now,it makes no difference.
Don't overthink things,try to understand your DS and respect his true feelings.
Sending a hug as I do know how the earlier days felt