To show that the PlayStation 4 launch event wasn't just about Sony's soon to be released console for those in Europe. They made an announcement about The Last of Us and how fans can look forward to a new chunk of story based DLC to be available next year.
The announcement may have potentially arrived a little late for PlayStation 4 purchasers in the US as they may have already traded in their PlayStation 3's in order to get the new console. At least it gives us in the UK a while to consider what to do, I'll be keeping my PlayStation 3, but others may not have that choice. On a side note I think a great announcement would have been to release The Last of Us on PlayStation 4.
The Last of Us: Left Behind will be released at an unannounced date during Spring in 2014.