Prince George Was Assissinated
The fourth son of King George V, Prince George of Kent, was rumored to be a Nazi sympathizer and drug user. When an aeroplane carrying the Prince crashed and burned, then, talks of assassination were rife.
Whilst plane crashes at the time were fairly common, the fact that little to nothing was released on the details of the accident was very suspicious. Spookier yet, the only survivor of the crash was ordered to sign an Official Secret Act, preventing him from talking to anyone about what really happened.