With its "terrible tusks and terrible claws and terrible teeth in its terrible jaws" the Gruffalo has fired the imaginations of millions of children in the 10 years since he first emerged from the deep, dark wood.

Its award-winning author, Julia Donaldson, has gone on to write around 150 books, one of which was inspired by her eldest son Hamish, whose troubled life was tragically cut short at the age of 25 when he took his own life.

This morning on Desert Island Discs Ms Donaldson talks movingly about Hamish, who struggled with the psychiatric illness schizoaffective disorder, and told the show's presenter Kirsty Young she is almost glad he died before she did.

"Hamish was very imaginative," she says. "He had an imaginary friend who came out of the mirror – his reflection – and this inspired a series of books about a very naughty princess called Princess Mirror-Belle."

Asked if she'd reached any conclusion about her son's choice to end his life in 2003, she adds: "Sometimes I think it was an almost unselfish thing. During Hamish's lifetime, when he was drinking very heavily and leading this terrible lifestyle, I used to think 'Oh no, when I die, and Hamish grows old' ... He was a very goodlooking boy and just the thought of him growing old and being some old wino – of course I didn't want him to die but I used to sometimes wish that he would die before us."

The Gruffalo, the cuddly monster for which Donaldson is best known, was based on a Chinese folk tale about a tiger, but Donaldson says she could not think of anything to rhyme with that. It has been performed as a stage show and made into a film, as well as selling around four million copies. Yet the Gruffalo wouldn't have existed without another of her three sons, Alastair.

"I had a few books published, but most of them were educational," she says. "I got halfway through and I did get stuck and I was going to give up. I told my son Alastair about this and he said 'no, go on mum, I think it's really good'. So he did inspire me to continue."

The Gruffalo was published in 1999 when Donaldson, who lives in Dunbartonshire, was 51. As well as becoming an established children's classic, it has turned Donaldson into one of the nation's most celebrated children's authors, whose other works include The Snail and the Whale, Room on the Broom and A Squash and a Squeeze.

"It's a lot of blood, sweat and tears," she says. "It takes ages to craft them. It is a labour of love."

Donaldson, who worked as a teacher and publisher before her success, also explains on the show that when she was a child her father developed polio and became confined to a wheelchair before dying of a heart attack at the age of 59. However, it is the death of her son that looms over her life.

"When Hamish died everyone was so sympathetic," she said. "But I don't believe people fully understood how hard it was during the 25 years of Hamish's life. We've a film of Hamish as a little boy and friends couldn't understand how we could watch it without dissolving into tears. But actually we would watch it and dissolve into tears during Hamish's lifetime, during the very difficult years in his late teens and 20s. Then we were grieving for that little boy. I just wish he could have had a better life."

Desert Island Discs is on Radio 4 this morning at 11.15am, and is repeated on Friday at 9am