Telling a young child about an autism diagnosis

Hello, my 4 and a half year old son was diagnosed with ASC a couple of weeks ago and I'd like some advice on how to share the news with him. In the report, we were told to introduce the topic by highlighting strengths and saying that these were due to autism. I tried to start a conversation the other day when he drew a picture and said 'that's my brain'. I reminded him of the assessment appointment and started to say that after she played with him, the doctor told us about some of the amazing things his brain can do. He wasn't interested in the topic, or didn't feel like talking about it at the time, so I didn't get any further. I want to be open with him and share his diagnosis but I want to do it in a sensitive and accessible way. I also understand that his understanding and feelings about himself will grow over time, so we can go little by little, but wanted to ask what your experiences were and if you have any tips / resources? Thank you!