"You're trying to do the best that you can do within the art form that you can do and the first thing that happened was I started working on it, and about three weeks after I started, she died."
Donovan says from a purely selfish point of view he was disappointed that he wasn't going to have the chance to work with Margaret, and he was also worried the publishers would can the book.
Fortunately, Harper Collins wanted to press on, and so Donovan went back to work.
Dashing Dog was actually first published many years ago, but Donovan says in the original version, the illustrations did not do the text justice.
"With Margaret Mahy's books, not all of them, but quite a few of them, I feel that the illustrators have let Margaret Mahy carry the weight of the book ... I've often thought the illustrations in a lot of her books are pretty cruddy."
Because of that, Donovan wound up spending around six months on his illustrations until they were the best he could make them.
"If I can do something brilliant with my art to match what she's with her art, that would be brilliant. I really tortured myself doing the art for this book trying to match up."
He says although Margaret didn't specify what breed of canine the dashing dog is, or where the story is set, she clearly had a great understanding of the relationship between author and illustrator, which Donovan says ideally is a 50/50 relationship where the author trusts the illustrator to add their part to the project.
"She doesn't confine me or control me or tell me what to do and it's such a lovely book to work on because she did her thing and I did my thing and I'm really proud of the work that I've done."
Donovan gave the dashing dog's appearance some thought and eventually decided the text suggested a large poodle.
It was not until later that he found out that Margaret had had a poodle and had written Dashing Dog about it, a coincidence Donovan finds amazing.
The illustrations in Dashing Dog are full of detail and Donovan says he hopes children reading Dashing Dog will discover new things at each read and feel the world inhabited by the dashing dog carries on beyond the edges of the pages.
He says what he loves about Dashing Dog is that Margaret takes the character on an arc where the dog starts out as a la-de-da kind of dog and at the end of the story is our hero, and it's all done in a deceptively simple way.
"Without the right kind of pictures we wouldn't get the full impact of all that, and I think that's kind of what happened with the original version.
"Often the pictures in her books are quite sombre and solemn and the pictures need to convey that real energy and silliness and fun that she has with the words and do that with the pictures."
Dashing Dog was released earlier this month and Donovan has also recently released another book, The Weather Machine.
Among the many projects he's currently working on is a comic novel, Monkey Boy, set during the Napoleonic Wars and featuring "warships, ghosts and people being slaughtered all over the place" which he hopes to publish next year.