Was Rupert Bear a spy?

Is it true that in one of the Rupert Annuals during the 2000's Rupert and his friend Bill join the Hitler Youth Movement? Someone told me that Bill and Rupert travel to Berlin and become involved with a group of Nazis. Rupert swaps his red top for a brown shirt and Nazi insignia. But true to the lovable character which Alfred Bestall created, Rupert and Bill are really undercover spies for the French Resistance who have a plan to assassinate Hitler.

I have not been able to verify this. Does anyone have any information about this or able to let me know in which year the story appeared?