By setting your computer or console's internal clock to the date of Rocksteady Studios' founding on December 13, 2004, and then visiting Calendar Man, special dialogue will play out where he talks about how he was there "from the beginning" and hinting at "the end of days". This Easter egg went undiscovered until November 10, 2014, when Rocksteady themselves launched a YouTube channel named "JG Jour", with only one public video uploaded hinting at the secret's existence without explaining how to access it. The profile picture of the account was a stock image of a calendar with the date July 17, but this date turned out to be a red herring. "Jour" is the French word for "Day", meaning that the channel's name and profile picture were only meant to strengthen the secret's connection to Julian Gregory Day (the real name of Calendar Man), and the puzzle was solved three days later on November 13. It's believed that the timing of this Easter egg's reveal was meant to reference the release of the then-upcoming final installment of the Batman: Arkham series, Batman: Arkham Knight.