Developer Mythic Entertainment is celebrating the 15th anniversary of massively multiplayer online role-playing game Ultima Online by overthrowing its in-game king, reports the game's official site.

The development team has set up a seven-month-long in-game event that will see the deposition of the current king and the coronation of a new one.

The team has also released several puzzle pieces of the past few days. What these pieces will unlock remains unknown. Mythic is also holding a costume party to celebrate the anniversary at company headquarters in Fairfax, Virginia. The two best costumes, one male and one female, will win a pair of Mythic games off the EA Store.

Ultima Online first launched on September 24th, 1997, and is the longest continuously-running MMO of all time.