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A boy’s mole grew so big that by the age of six it covered his entire back like a turtle’s shell, earning him the nickname of Turtle Boy.

The rare birthmark - congenital melanocytic nevus – affects around 1 in 20,000 newborn babies but a top surgeon described Didier Montalvo’s condition as the worst he’d ever seen.

Didier’s life was severely affected by the growth, covering more than half of his body circumference, both in the painful itchiness of his skin and how it affected his confidence.

He and his family were shunned by villagers in his home in rural Colombia in South America and his mother Luz was even told it was her fault for looking at a solar eclipse while pregnant.

(Image: Channel 4)

The family were too poor to shell out for surgery - but his life changed when his touching story was featured in a local newspaper and a flood of donations poured in.

While they could now afford the op, the life-changing surgery was still by no means straightforward – in fact it would be painful, dangerous and complicated.

A Channel 4 documentary tonight will see a plastic surgeon from Great Ormond Street Hospital in London go over to Colombia to help the team operate.

GOSH surgeon Neil Bulstrode has operated on dozens of children with CMN – but never one as extreme as Didier’s.

He said: “Didier’s CMN was the worst case I had ever seen due to the size and bulk of the lesion.

“Effectively three quarters of the circumference of his body was affected.

“Often people have CMN that are much flatter and are therefore much easier to care for and deal with.”

However, it did not stop Mr Bulstrode wanting to help remove the growth - and let Didier ditch the Turtle Boy nickname.

Mr Bulstrode added: “When I saw the pictures of Didier, one of my first feelings was that if we could remove it, we would significantly improve his quality of life.”

(Image: Channel 4)

The full drama of the surgery will be seen in the documentary tonight but as you can see from this picture there is a happy ending.

Mr Bulstrode said: "It was great to be able to pass on our knowledge and skills, helping to get a great result for Didier.”

GOSH paediatric dermatologist Dr Veronica Kinsler runs a weekly clinic for patients with the condition.

She said: “When babies are born, their parents can get understandably very worried until they know what the marks are.

“In the weekly clinics we run at Great Ormond Street Hospital we are able to give a diagnosis, check that the moles themselves are safe and whether the skin appearance is telling us what other things might need to be checked. “

* Turtle Boy: A Bodyshock Special is on Channel 4, 10pm. For more information on CMN , click here.