Update: A new trailer for the Gran Turismo 15th anniversary ends by scrolling through the Gran Turismo games - 1 through 5 - before stopping on an underscore which hints that a new numbered game is coming.
Original story: Sony looks set to reveal Gran Turismo 6 on May 15 after invites for a 15th anniversary event went out today.
Posted to NeoGAF, the invite states: "Join us to celebrate 15 years of Gran Turismo, and discover exciting announcements about its future."
The event will take place at the Silverstone Circuit in Northamptonshire.
Sony has previously gone on record stating Gran Turismo 6 will be released for PS3 this year, but there remains chatter that the game could also appear on PS4.