How to tell my child!!!!

My son is 9, and I've known for a while about him having autism. I never told anyone as I didnt want him to feel any different to the other children. His school has asked me to attend a meeting this week to discuss their concerns as they think he has autism. I feel like the worse mum in the world as I've known since his doctor told me but I kept it secret :-(. I thought I was protecting him but now I have to tell him. He is such a quiet, emotional boy and I'm scared how he will react. His school have been great,and his teacher said she understands why I've not said anything, but she's said he will get all the help he needs and more and I should think about the positives instead of the negatives. I'm also looking for help on how to explain to my son about all of this. He really doesnt handle change well :-(.

Hi, before my son got his diagnosis we said we didn’t want to tell him because we didn’t want him to think he was different, but the truth is he already knows he is as he tells me a lot that he is not the same as other children. So when we did get the diagnosis we have decided that it would be good for him to know and understand as much as possible, we are going to talk about it over the weekend as he will be with both of us if he has any questions, I believe it will be a good thing for him to know especially as the differences are becoming more apparent as he gets older x 

Hi, before my son got his diagnosis we said we didn’t want to tell him because we didn’t want him to think he was different, but the truth is he already knows he is as he tells me a lot that he is not the same as other children. So when we did get the diagnosis we have decided that it would be good for him to know and understand as much as possible, we are going to talk about it over the weekend as he will be with both of us if he has any questions, I believe it will be a good thing for him to know especially as the differences are becoming more apparent as he gets older x