Dylan Siegal found out friend Jonah Pournazarian suffered from glycogen storage disease type 1B when he was just six.
But he decided that he was going to raise money to find a cure for his best pal – so he wrote a book.
The book, called Chocolate Bar, has so far collected £635,000 and is all about ‘what’s awesome’ to Dylan.
In the book he says: “I like to help my friends. That is the biggest chocolate bar to me.”
Jonah, 9, is only one of 500 children in the world suffering from the incurable disease.
Those who have it mean their livers can store sugar but not release it. This causes low blood sugar levels, which can lead to seizures and death.
Of his best friend’s selfless gesture, Jonah told reporters: “I felt good when my friend was trying to help me so I could get better and feel like other people.”
And Jonah’s mother Lora is just as grateful. She said: “Dylan has touched us so much. It’s beautiful.”
Because of his condition, Lora has to feed him a corn starch and water mixture every night at 3am.
She said: “A huge anxiety every night [is] we go to sleep going, ‘We hope we don’t miss an alarm clock because he could die.’”
You can donate to Jonah’s cause or buy Chocolate Bar here.