Explaining to my son

Hi,

My son is 10 and has for a long time thought and said he's different.  He was diagnosed ASD around 3 years ago but hasn't been told.  I am working with the school and Autism Outreach to tell him about his diagnosis but I'm struggling on how to approach the subject with him. Can you recommend any books that I could read and maybe read with him that would help? Or do you have any tips for me.

Thanks