The original Dutch novel "De Brief voor de Koning" was written by Tonke Dragt in 1962. It was adapted in Dutch as De brief voor de koning (2008) twelve years before.

Filmed in New Zealand and the Czech Republic.

The series is adapted from a Dutch novel by Tonke Dragt written in 1962. Although translated in many languages, an English version wasn't available until 2014, but its popularity in the UK was the engine behind this series adaptation, nearly 60 years after the book's release.

Author Tonke Dragt was consulted on the adaptation of her book and approved of most of the changes, such as expanding or condensing characters, and bigger roles for women. The inclusion of magical elements was taken from the novel's sequel, 'Secrets of the Wild Woods' (where it features more subtly); Dragt reluctantly accepted it, stating that she "probably would have put up more of a fight, had I been younger". The only thing she outright vetoed was the initial removal of the character Piak, who was added back in subsequent drafts.