As a S/O to Mr Bee's threads about the saddest tv episode and saddest songs, what is the saddest book you've ever read?

I just finished The Light Between Oceans and sobbed my eyes out. I mean, literally sobbing with red, puffy eyes and gasping for breath, it was awful. I just wanted to hold my toddler so close and never let her go.

What books have you read that have hit you to the core emotionally?