WWE has an updated poster for next Friday's "Greatest Royal Rumble" event on their website, which you can check out below. It confirms that Rey Mysterio will be participating at the event.
Other non-full time stars featured on the poster include The Great Khali, Mark Henry, Shane McMahon, Kurt Angle, Chris Jericho and The Big Show. Jericho, Angle and Big Show had been previously announced for the match.
Below is the image that appears on WWE's official website:
Here is a closeup of just the poster: