A long decorative frieze bearing knights in armour, Red Indians and Scouts was uncovered by chance in an unused corridor of his old school in Brussels, after someone decided it should be redecorated.

Such is Hergé’s following that the mural is now expected to become a pilgrimage site for his millions of fans worldwide. Tintin is a cultural icon. His cartoon adventures have been translated into more than 50 languages and sold more than 200 million copies.

Michael Farr, who has written a biography on Hergé due to be released this week, described it as a particularly exciting discovery. He said: “Hergé’s first published stories were of a Boy Scout leader called Totor, a precursor of Tintin. This is very much in the manner of that.”

Totor, an adventurous Scout and leader of the Maybug Patrol, was modelled on the artist’s own Scouting experiences and was to be the prototype for Tintin.

The mural’s discovery coincides with the centenary year of Hergé’s birth, just as Steven Spielberg and Peter Jackson are planning to bring the adventures of Tintin to the big screen.

Totor, Patrol Leader of the Cockchafers (Maybugs) is the first comic strip series written by Hergé, who later wrote The Adventures of Tintin.