The next day, they tell Hazel's mom a funnier version of the Peter Van Houten story.
Hazel's mom leaves them so that they have time to talk. Seems weirdly ominous, right?
They walk back to the hotel and Hazel is terrified, obviously, because Augustus has something big to tell her.
Augustus sits her down and tells her that he recently went in for a PET scan… and it wasn't good. His cancer has returned. They are both utterly devastated—and in love and sad and heartbroken. They are, essentially, feeling all the feelings.
Many tears are shed and Augustus promises that he'll fight that cancer as hard as he can for her.
Also, the reason he was fighting with his parents was because they wanted him not to go to Amsterdam so he could keep up with his chemo treatment.
Augustus is sad that he will never have his epic fight, the thing that will give his life meaning.
Hazel tells him that he gets to battle cancer.
Then, after all the serious talk is over, they make out. Duh.