Callie Blackwell Boy in 7 billion

As seen on ITV1's This Morning.

This is the agonising and emotional book that everyone is talking about.

A powerful true story revealing a remarkable relationship between a dying son - and a mother that refuses to let him go.

At the age of 10, Deryn was diagnosed with Leukaemia.

Then 18 months later he developed another rare form of cancer called Langerhan s cell sarcoma.

Only five other people in the world have it.

He is the youngest of them all and the only person in the world known to be fighting it alongside another cancer, making him one in seven billion.

Told there was no hope of survival, after four years of intensive treatment, exhausted by his fight and with just days left to live, Deryn planned his own funeral.

But, Deryn's desperate mother, Callie would not let him give in.

Battling medical errors, impossible odds and years of hardship as the cancer consumed his body and their world, they looked for more answers.

After making some startling discoveries and taking massive chances - something began to change.

Would their lives as a family ever be the same again?.