The RAF museum archives tell us the story of the phrase “Beware of the Hun in the Sun!” The archive story describes the origin of the phrase.
“One of the most famous phrases in aviation history, and a lesson which is as valid for today’s military pilots as it was in the First World War. A cunning fighter pilot will always try to use the sun to blind his opponent.
Collection Ref: X001-4358”
Super Sabre pilots probably have added thoughts to this maxim!