Minecraft wiki entry for Combat_Update, associated text: As the trend has been since version 1.2, the update notes say "Removed Herobrine", despite the fact that Herobrine was never part of the game.
The name for the update was teased in the joke snapshot 15w14a with a QR code.
This is the only update to date that released on leap day (February 29th) and is guaranteed to remain that way until at least 2024 (assuming no alterations are made to the calendar).