Where did this one come from? Well having done a bit of research there appears to be a split between the changing of the Julian calendar to a Georgian one, or when the French King Charles IX changed new years day from April 1st to January 1st. No we have to say that our bets are on good old King Charlie as only a fool would be caught celebrating new years day 3 months after the event. Anyhow, which ever one you go with, you just have to love April Fools Day.
