WWE just announced that Chris Jericho will be replacing Rusevin the Casket Match against The Undertaker at the April 27th Greatest Royal Rumble event in Jeddah, Saudi Arabia, which will air on the WWE Network.Jericho was previously announced for the 50-Man Rumble match that is taking place that night.
The storyline is that Lana refuses to let Rusev compete in a Casket Match. She made this tweet shortly before WWE announced the change:
 

All over the world, little boys and girls are celebrating #RusevDay, they smile for the greatest Superstar ever ! I’ve already spoke with @WWE officials to change that match because I REFUSE to let my husband @RusevBUL compete in a Casket Match at #WWEGRR! Happy #RusevDay
— CJ (Lana) Perry (@LanaWWE) April 12, 2018

I beat #TheUndertaker for @wwe title before. At #GreatestRoyalRumble, I’m gonna BURY his ass…#KingOfTheCasketMatch pic.twitter.com/rLThP1lJgC
— Chris Jericho (@IAmJericho) April 12, 2018