Blimey, it's hard to believe that Angry Birds is four years old, isn't it?

It feels like only yesterday that Rovio released its humble phenomenon onto the App Store, and then quietly revolutionised mobile gaming forever.

Anyway, to celebrate the occasion, Rovio has released a brand new 'Birdday Party' episode for the original Angry Birds on both Android and iOS, which contains 15 new levels.

Four years on, another reason to revisit Angry Birds. Say what you will about Rovio, but you can't knock that lifespan.