How to talk with 4 yr old about death/loss

I think our 10 year old lab is sadly not far from his final days and I want to talk with my little one about it so it’s not a surprise. after some research I ordered the books “the invisible string” and “ida always”.

I’m a very emotional and empathetic person and I just know I’m going to cry talking about it and reading the books and he’s never really seen me cry that I can remember.

I know it’s an opportunity to talk about emotions, life, death etc and I want to tell the truth in a way that makes sense to a young kid.

If you have handled this before can you share what you said?