Century-old LEMON used by German spy to send secret messages from Britain in invisible ink during WW1 goes on display

A 110-year-old lemon which was used for writing secret messages with its juice, and formed evidence to convict and lead to the execution of Karl Muller for spying for Germany in World War One is displayed, which forms part of ‘MI5: Official Secrets’, a new exhibition exploring the history of the British intelligence agency, at The National Archives in London, Britain, April 1, 2025. REUTERS/Toby MelvilleReuters

A 110-year-old lemon used by a German WW1 spy to send secret messages...