Based on a book by Astrid Lindgren, author of "Pippi Longstocking". Lindgren wrote the book after she saw a lonely boy sitting on a park bench in Stockholm. She wondered what he was doing there, who he was and where he would end up. That gave birth to the story of Prince Mio. The bench which the boy sat on can still be found in Stockholm today, marked with a sign saying that "Mio sat here".
The Chernobyl disaster of the power plant occurred at the same time they were filming. The crew completely evacuated the area, however came back to shoot the month after. They had numerous Geiger Counters set throughout the shoot to monitor radiation levels.