Up until the age of 7, my best friend was a girl. Then we moved house and I never saw her again.
When I told my mother I was trans back in 2001, I was 28 yrs old.
She (and my father) both said afterwards that they thought I was going to tell them I was gay, nope, surprise!
My father got his head around it in about 30 mins (I was always very close to my dad), my mother did not!
She got really upset with me, and cried "I could have understood if it had been your brother, but not you!!??"
See, my brother was arty, like my mom, he was great with children, good at cooking, outgoing and confident, and he worked as a primary school teacher. He always got on really well with my mom, whereas I did not.
I was shy, introvert, unhappy, severely depressed (multiple suicide attempts by that point), not good socially or with people, mechanically minded, and ended up as an engineer. So in her eyes, my brother 'should' have been the girl, and I should be the boy.
Sigh, if only it was that easy mom...
It took her 6 months to finally come to terms with it, and agree to meet me again.
Through all of this, I was still in contact a lot with my dad, and he was always telling me to just be patient and give her time, so I did.
When I finally met my mother again 6 months later (this time I was dressed as female), she told me that actually there had been some very subtle things that I had done as a child that she had dismissed, but now she though about it, she could see why. Things like how I always wanted to grow my nails long and shape them in a feminine style, which she always forbid me from doing, to the point of forcibly cutting them. Also she was forever picking me up on how I walked, and saying that it was 'wrong' and that I should walk 'properly', i.e. in a more masculine and less feminine way.
She also confessed that some reasons why she had struggled so much once I told her was that she blamed herself for "causing" my gender dysphoria because she might have done something wrong while she was carrying me, or been too stressed and caused the hormones in her baby to get mixed up. I told her that it was not her fault, and she couldn't have caused it, but I could see it really bothered her. Also, she said she had had to grieve over the loss of her eldest son (me) as she felt like 'he' had 'died' and been replaced by a woman. She said she had to do this to come to terms with it, and be able to "swap" her son for her daughter.
She is absolutely fine about it now, and only treats me as her daughter, we go shopping, and are much closer now than before I transitioned.
I am actually really impressed with how my dad coped with it all. He just seemed to flick a switch as suddenly he had a daughter, and that was that. No fuss, no bother, he just got on with it. I'm very lucky as I have heard so many trans people say how their fathers have not accepted it at all.